What's the point of Aggro mobs?

[Shampooo]

I mean if you just run for 10 seconds and you're in the clear? I think they should get rid of "XXX returns back to its territory. I mean even if you do die there's no penalty. There's no danger, i want danger.

Think of them like fat cops, they start chasing you and your gonna run, but you know they'll only run so far =p