What makes push mail better than non push mail?

[Stingray]

Please don't flame me for this.... I am kinda new to the world of Windows Mobile... I have somehow managed to make push mail work on my 6700....
But I still have a question... What makes push mail better than non push mail? I hear that it drains less battery, but why? I think it should drain more battery since it always keeps a connection open with the exchange server?
I'm not even sure if I'm using the right terminology here...