Many times, pc's get separated. Roll20 in its current form doesn't seem to be able to handle the task. All pc's stay on the current map. If one gets transported to a different area, or had to complete a task on his/her own, all the pc's as far as I can tell, have to follow. I think the ability to put players on different maps would be a great feature. That is, with the ability to make sure that only the pc's to see only the map that pertains to them.
Separate maps, sub-campaigns? Something like that could be possible I think.
Thank you