How useful is the GRE for the academic career/research/daily academic tasks?
It's not required in my country but I'm wondering about the intrinsic value of its study material.
The GRE's effectively only good for one thing - getting admitted to graduate school. You will need it if the program requires it as part of your application package. Most US graduate programs do require it. If you study elsewhere then there's a good chance you don't need the GRE.
About whether it's useful study material, note that the GRE is an exam, not study material. You can use the GRE as a benchmark to see whether you're mastering the study material, but not as the study material itself. As for whether it's useful, knowing more things is usually never worse than knowing fewer things. However, will knowing more about undergraduate-level e.g. physics or mathematics help you in your career/research/daily tasks? If you teach physics or mathematics, then presumably so (although at that point you probably don't need the GRE because you are already intimately familiar with the material), or maybe if you work in science communication, provide private tutoring, etc. In most careers though, it will be irrelevant, and you can ignore the GRE.
We should distinguish between the different GREs.
The general GRE has three components:
There are also subject GREs in physics, math, and other subjects. These are specifically designed for those applying to graduate school in the respective subjects. The physics one allocates 1.7 minutes per question on average. Obviously this is very different from research, where you can spend months working on one problem. Still, this does have some loose connection with your familiarity with certain basic concepts.
TL;DR: the general GRE has limited usefulness after you get into grad school and is difficult to study for, so I do not recommend spending time on it. Possible exception for the writing section. Studying for the subject GRE is not a bad way to review certain basic concepts that you may have forgotten, but success on the subject GRE is only loosely correlated with success in research; they are fundamentally different endeavors.
Any exam is really only useful for whatever organizations look at scores on that exam, so the GRE is itself mostly just good for getting into graduate school. Of course, it could in principle also be used to judge for yourself whether you have the competency necessary for graduate school.
That said, there is some evidence to suggest that success on the GRE is a poor indicator of success in graduate school, and many graduate schools are dropping it as a requirement. What that means is that the GRE may not be particularly useful as a metric, for yourself or others, regarding your ability to handle graduate school in your chosen field.
tl;dr- If you're planning to go to grad school for one of the fields that has a subject-specific GRE, then the review materials for that subject-specific GRE might be helpful to you. However, the standard-GRE is more like an aptitude test (sorta like an IQ test); it's unlikely to be worth reviewing unless you're just curious how you'd do to boost your confidence.
There are two main types of GRE:
The standard GRE.
If someone takes any GRE, they likely take this one. It's mostly meant to be an aptitude test.
Subject-specific GRE exams.
These exams focus on specific subjects, usually for students who want to get a graduate degree in that subject. For example, the Math-GRE is for prospective Math graduate students.
In the United States, prospective graduate students are commonly required to take the standard GRE. Some departments additionally recommend/require a subject-test.
It's worth stressing the huge difference between these.
For example, there's an "Quantitative Reasoning" section on the standard-GRE that most people just call the "Math section", but the most advanced math is stuff that most students should know long before graduating high-school. Any student going into a mathematical field should find the study materials to be utterly trivial, or else they're probably in trouble.
By sharp contrast, the subject-GRE for Math is designed to test Math majors on what they should've learned in college. From the official website:
The test consists of approximately 66 multiple-choice questions drawn from courses commonly offered at the undergraduate level.
Approximately 50 percent of the questions involve calculus and its applications — subject matter that is assumed to be common to the backgrounds of almost all mathematics majors.
About 25 percent of the questions in the test are in elementary algebra, linear algebra, abstract algebra, and number theory. The remaining questions deal with other areas of mathematics currently studied by undergraduates in many institutions.
Unlike the standard-GRE, someone who wants to get a PhD in Physics or Engineering could do poorly on this Math test while still being adequately prepared for their PhD program.
There're three parts to the standard-GRE:
If I recall correctly, it's mostly a lot of vocabulary questions. They call it "reasoning", but I think the logical aspects of the questions are pretty trivial if you know what the words mean. But, many of the words they choose aren't commonly encountered in regular or even academic texts.
This is the "Math section" of the standard-GRE. The math in it's really basic; you probably learned the basic math in early elementary school (Ages 5-7 in the US), while the most advanced math is more middle-school-level (Ages 12-14 in the US).
This is the "essay section" of the standard-GRE. I think the goal's basically to show that you can write a short essay on some topic. Its grading seems more subjective than the prior two sections'.
Study materials for these likely aren't too helpful. Because:
The verbal reasoning (vocabulary) section can be studied by memorizing lots of vocabulary for words that many people don't know specifically because they're rarely (if ever) used. Your time could be better spent by studying just about anything else; I'd put this knowledge as being about on-par with Dungeons and Dragons (D&D) trivia.
The analytical reasoning (math) section is just basic math stuff. I think most people should be able to ace it if time weren't a factor. If a student were to find this math study-worthy, then they may not be right for graduate-level studies.
The analytical writing (essay) section has test-takers write a short essay. If any part of the standard-GRE is worth studying for, it might be this one, just because it's practice in basic communication. However, I'd suggest that if you want to practice this material, you might want to try writing some good questions/answers on StackExchange instead.
At current, there seem to be 6 subject-specific GRE's:
If you're preparing to enter graduate studies in one of these areas, or else you're just interested in what undergrads in those areas often study, then it could be productive to review the study materials for them.
For example, if you're interested in getting a PhD in Physics, then you might want to look over the Physics-GRE to review what you may've covered in undergrad and may see again in grad school.
However, even though Physics is a math-heavy subject, you don't necessarily need to worry about the content on the Mathematics-GRE, which would be more of something for a prospective Math graduate student to review.
The GRE is useless as anything but a filter for applications. For instance, the ability to do middle school level mathematics in a 1 minute time frame does not reflect on the individual's ability to do higher level mathematics research and produce innovative things, as long as they have a background.