Can't switch between workspace 1 and 2 on my right monitor while leaving my left one on workspace 3. In fact, I believe by default I wouldn't even get workspaces on my secondary monitor. Because who needs 'organization' anyway?
Gnome works OK with integer scaling, more granular than this and you're up shit creek.
E.G. can you set one screen to 150% and one to 175%? (I think the answer to this is 'technically yes but then everything goes a bit blurry because they do it by rendering at 2x then downscaling')
Proper mixed dpi scaling means stuff will render pixel-perfectly instead of downscaling hacks.