Allows to permanently disable one or several of the following HUD parts:
Floating damage numbers when hitting spells
Floating status effect when hitting spells ("RESISTANT")
Floating objective markers (main quest & open world activities)
Regarding objective markers
For active main quest, I recommend using Cuff Compass (in Accessibility Settings) to display a trail on the ground when you use Cuff Scan. Note that both of these may not be available at some points in the game (mainly the intro).
Personal markers are not affected, so you can still set up to 5 on the map for open world objectives or journal quests. Also not available very early game.