My advisor suggested including a simple plot in my physics PhD personal statements for US universities in order to make the essay more interesting and give a bit more detail about a research problem I am working on right now. On one hand I agree that this would probably make the essay more interesting, but I am concerned that the admissions committees would be annoyed since it will take them a bit longer to look at and understand the plot. Is this a good idea?
I would much prefer that the applicant give me a plot to look at than that he tries to explain everything only in words. A balance of text and graphics can be beneficial in many pieces of academic work. Adding a graphic may actually speed up the understanding of an applicant's application materials. This is why most of us can read a comic book much more quickly than a novel. I am actually more prone to drifting off while reading paragraph after paragraph of text with no "graphic relief."
As academics, we are quite used to being told to refer to figures. If an explanation of your work can be aided by use of a graphic or two, by all means please include them.
At the very worst, if someone feels they only have time to read text, they can just ignore the graphics. This would likely be to their own detriment.
You're starting from the wrong end if you're asking whether per se, a graphic is bad. The question you ought to ask yourself is: Given that I'm trying to explain a concept to the reader, what is the best way to do this. If a figure is the best way to explain things, then add one. If the figure does not add anything that's not also easy to explain in text, then omit it.