A big workflow in modern Photoshop is stuff like Layer Styles (non-destructive image editing). GIMP has no equivalent to that (most of its filters are still destructive, despite the 10+ year project to switch to GEGL).
There's plenty of other weird awkward UI and mental model decisions (e.g. GIMP makes the user select the width and height of each layer up-front, when Photoshop just assumes an infinite canvas and computes an AABB for each layer, leading).
A good portion of the work I do in Photoshop is vector editing (e.g. any real composition has dozens of shapes and even purely pixel work is going to use a lot of vector masks), GIMP lacks any vector tools and the team has been opposed to adding it, because it thinks Inkscape is better suited to vector art. Which, I mean sure, but it misses the point! Vector masks are incredibly valuable for compositing work, and we shouldn't have to switch between two radically different apps to have a usable workflow.
There's plenty of other weird awkward UI and mental model decisions (e.g. GIMP makes the user select the width and height of each layer up-front, when Photoshop just assumes an infinite canvas and computes an AABB for each layer, leading).
A good portion of the work I do in Photoshop is vector editing (e.g. any real composition has dozens of shapes and even purely pixel work is going to use a lot of vector masks), GIMP lacks any vector tools and the team has been opposed to adding it, because it thinks Inkscape is better suited to vector art. Which, I mean sure, but it misses the point! Vector masks are incredibly valuable for compositing work, and we shouldn't have to switch between two radically different apps to have a usable workflow.