If players spread out over the maps... consider this
Each player needs to send their data to all the other players.
So which would use more bandwidth?
20 users in one map (20x20) = 400
or
20 users split between two maps (10x10) + (10x10) = 200
That is the right way to look at it, right?
When more people join a single map, the needed data transfer becomes
exponentially higher! (1x1, 2x2, 3x3...)
Spreading out across the maps WILL help the server load.