Here's why I still find layers useful. Say I'm placing door and secret door symbols. These both go on the SYMBOLS sheet. I put the doors on the Wall Features layer and the secret doors on the Secret layer. Now I can hide the Secret layer and print out a players' map and the secret doors are not visible to them. If I hide the SYMBOLS sheet, all symbols get hidden.

Sure, I could create a SYMBOLS DOORS sheet and a SYMBOLS SECRET DOORS sheet and then hide the latter before I print the players' map. But what if I'm using sheet effects? I would then have to duplicate the same effects on both sheets, and that would take more time. Even if that could be improved on (like by doing it once and saving the sheet effects to pull up again in another map), I kind of like having the multiple options of ways of doing things that CC3 provides in full.