Hiding stuff on GM layer works well on most situations but every now and then we have a situation where some PCs can see something but some can't and I as a GM have to choose whether to show it to all players. If tokens would have an option for who can see it, this wouldn't be a problem. This could be in the same form that "Can edit" is. You could for example properly represent a situation where an enemy is invisible but one PC has see invisibility. The controller of that PC would actually have to try to verbally give directions/guide to the other players/PCs. The most common situation where this would come in handy for me is in campaigns that are in Warhammer world and there is a PC with witch-sight (skill magical sense) in the party. In many occasions these PCs don't want to tell what they "sense" or at least leave something out. Nowadays I use private messages through Steam to describe additional information but most of the information could easily be included on the Roll20 page if I could manage who can see and what.