I've used Gimp all through my teenage years. And I used it a LOT. It was quite a difficult transition to Photoshop (which my workplace uses). But once I got the hang of photoshop, I realized how convoluted Gimp really is.

Half the time spent in Gimp is making backups before making an edit. A third of your layers will be backup layers in case you change your mind about a design decision. The whole design process is super inflexible and therefor kills creativity.

Want to use an effect like gaussian blur or drop shadow? Make sure you backup your layer! Want to edit text after you stretched it all out? I hope you made a backup of that layer! Want to work with large files with many layers? You better hit ctrl S after every edit, because the program just might crash on you if you make a difficult selection!

To be fair, I haven't used much Gimp since 2.8, so if stuff is different now: awesome! And I admire all volunteers that work to make stuff better. But for now, I'll stay away from it if I need to do heavy editing.