VTT Foundry has an option with which the GM can give access to multiple map pages to players so they can move between maps, such as going in and out of a building or a cave, as they please and look back at already explored maps to gain information they might have forgotten.
I think it would be a useful addition to Roll20 if the GM would decide what pages to give access to and could withdraw access later on if the players meant to revisit the map with changes on it.