The yellow paint is only really necessary in the event they aren't given enough a time in the design phase. If everything works correctly, you should be drawn towards the correct way to go by visual cues. Having the yellow paint means it's not necessary to indicate with those visual cues which make for a less planned out environment. It is at best a crutch so that game designers can focus on more important things. It should not be seen as an end to itself.

This breaks down for lots of open-world games, although the linear dungeons can absolutely still be done without the line.