I use gimp because... well, it's free, and solved many problems for me in terms of hardware, software, and... it is much more stable than (read.. much older) versions of Photoshop. To be fair to Adobe, it's possible that their "student" edition was lobotomized and therefore less stable. But I also think that it uses resources more efficiently.
I also think that it is easier to use, too, but again, my experience with Photoshop is old. 1996 old. ;-)
In fact, I avoid Adobe now because it doesn't run on Linux.
Ok, ok, fine... I could get macOS, which is technically a flavor of unix... but... I like Linux better. Again with efficiency. And black boxes scare me. At least technical ones. Black is a fine color, and boxes are pretty cool. But technical cat in a bag is just. not. cool.
If it breaks, I want it to be more than theoretically fixable by me. Sure, I'm not the biggest hacker on the block, but if I or one of my more technically minded friends can't look at the problem because of some big mega-corp's say so, (even if it's fuzzy Apple) then it's time for me to take my toys and go home.
What do I use it for? Well, I make maps and other visual aids for old-school, pen-and paper, dice and pizza style RPG gaming. This way I don't have to write an API.
I also touch up photos I take IRL (I live near a big city, and LOVE my Rebel!) And, when I make jewelry and sell it, I mod those photos, too... mostly to alter for the web, color correction, and cropping.
I also make graphics for the web... maybe for my next blog. Not sure yet. Graphics tend to take me forever to finish, and... suck me in. So graphics happen, but no blog post. Like that.
I also make collages and stickers and so on just because I can.