The difference is what happens when their plan fails? If a group is trying to be sneaky and they're found, do they press the attack or do they vanish and go looking for the next undefended base? Depending on the answer to that question, it affects how people on the other side perceive them.
It's the same with an alt monkey or hordeling. If the person preferentially comes in above the enemy or one of many, the difference between them being a decent fight or annoying is what they do when they get there and someone's higher than them/the enemy are more numerous. If they fight anyways, it's fun for all. If they don't, the game devolves into "Runner Chaser III".
Wiley.