TL;DR: GET RID OF IT.
It's unnecessary. It's worthless. Here's why.
It DISABLES skills, not just visible UI elements.
Seriously. Here's a list of what can be used while it's active: the slot 1 skill, via mouseclick only, tab- and mouse- targetting, and basic 4-direction movement. everything else, including screenshots? completely disabled. And I mean everything. Not even the ESC menu is available while Ctrl+U is active. It cannot be unmapped or remapped to a different key.
This makes it problematic as it can far more easily be accidentally pressed, unlike Ctrl+Z which (a) is better and (b) can be moved to something not next to actually important keys. Speaking of... It's redundant.
There is already another "disable UI" option (the one that defaults to Ctrl+Z) that can be mapped to any key and, more inportantly, unmapped entirely. All in all... It's not a feature, it's a problem.
No one is going to use it and if they do, they'll use the version that can be mapped to any key they want, that also doesn't disable skill hotkeys. This one's only use is to re-enable the UI after someone accidently disables it by pushing this button.
It's SO rarely used that we mostly just forget about it. I did. It got me killed during an otherwise perfect eternal championship run for the Deathless Champion title because I couldn't remember that this so-called 'feature' existed. I had to instead force-close the game (alt-F4) and restart, logging in to find myself dead in the arena. I'm sure i'm not the first.
So, what do you do with a 'feature' that causes more harm than good, cannot be turned off, and has a better version available without these problems? GET RID OF IT. It's not even a difficult fix, just take out the hotkey mapping that ties it to Ctrl+U. Please. This shouldn't even exist in the game to begin with.
