I am not in any admissions committee, so I am more or less guessing here.
A MOOC shows you have interest in the subject, and that you have a basic knowledge (you are familiar with the topics and some vocabulary). This knowledge is very easy to test in an interview by a few basic questions, so having a signed track will not add much to it.
Nevertheless, the skills learned during the course can be a good point if they are a good complement for your degree. For example, if you are a physicist wanting to get into experimental data analysis, knowing machine learning is very useful; but most Physics programs do not include this as subject. On the other hand, taking a programming course for a CS adds next to nothing.
An advantage of MOOCs is that you can take them for free, and you can just sign up for several of them just to see if the topic interests you, so they have a very low cost of opportunity. If you sign up for a university class, you have to pay for it (depending on the country) and/or actually see it to completion. Even if you find the topic too hard, too easy, completely irrelevant, or poorly taught.