Well, it'll take about 10 seconds longer to generate than a standard sized map 
Depending on the mod (I'll assume Wild Mana for you) you'll end up light on the jungles since you'll only have 1 civ out of 21 with a preference there. Deserts and tundra will also be reduced due to the relatively low number of civs prefering those climates.

Depending on the mod (I'll assume Wild Mana for you) you'll end up light on the jungles since you'll only have 1 civ out of 21 with a preference there. Deserts and tundra will also be reduced due to the relatively low number of civs prefering those climates.