>>24794054
At a minimum, it's to stop your reader from imagining the wrong things.
>Here is Sam. Sam likes to drink beer while watching NASCAR, hit things with rocks, and shout ooga booga. (5 chapters later). Sam blushed, because it was time for her period.
Here, the reader starts off thinking Sam is a rather caveman-like guy, and when it's shown that Sam is a girl, the reader is jolted and has to reimagine Sam as a girl, which is annoying.

I am of the belief that the lazy ass reader can go imagine all the details on his own. But clearly there is no upper limit to description, since Tolkien does a lot of it in The Two Towers. Also it would be funny if you put in non-necessary descriptions as footnotes.