Generally the random maps are chosen for each match in MP (so for 1v1 random small, 2v2 random medium, 3v3 random medium large, 4v4 random large and 5v5 random huge (or sometimes random huge ring). Always its in a single star system. These maps are considered best for team games since no one will end up with a certain advantage over other players, like what happens in maps with fixed starting positions.

Besides that, you always have to adapt to where you start in random map games, which makes them more fun to play.