There are a number of aspects of the game that only make sense on tiny maps:
Research speed.
Number of trade routes.
Kyrnn super ability.
Drengen super ability (at least I think its the Drengen. The one where they get a bunch of free ships.)
The price increases of researching spies.
Spy on every Planet Mega event.
How the AIs declare war on opponents across a large map that they could not reach in 100 turns.
How the AIs invade planets (sending all their rescources halfway across the board when that have much better targets that they can actually reach.)
Influence borders not being correct on reload (and other reloading problems.
There are others I can't think of at the moment.
All of these features work perfectly for tiny maps and are completely unballenced for large+ maps.
Scincerely,
Scintor@aol.com