Most of this has been said above, but -- oh, yes, quite frequently. And that can include horror and thrillers, by the way, as a good book relies on much more than a "surprise" or "shock" ending or twists and turns, and many of those things may not be picked up on upon initial reading.
I have a TBR pile that it's going to literally take me a couple of decades to get through... yet I will continue to also reread various books. I've read most of Lovecraft so many times I've lost count; quite a lot of Robert E. Howard multiple times (I've no idea how many);
LotR at least 20 times,
The Silmarillion at least 12; various other books are in that range, while some I've only reread between one and three times. (Of course, if we include my early childhood, I've read
Frankenstein,
The War of the Worlds, and
I, Robot probably upwards of 50 times each......
)
Revisiting old friends, discovering new facets in those old friends, finding new layers of meaning in them, having a new appreciation for the sheer artistry of the writing... there are lots of reasons to reread a book ... not to mention that, as you grow in experience, you bring that growth and change of perspective to anything you reread, and that plays a part in how you view the book (or watch the movie) as well... unless it's among the shallowest of books or films. (And even then this can be said to apply as, once you've read it, you can no longer go back and see it as entirely new, and so it's spoilt for you.)
Of course, this only applies to fiction. For nonfiction, there are many additional reasons as to why one might want to reread them, as learning, experience, etc., can increase one's understanding of the concepts or facts dealt with within them.....