What's with the body slams?

So, I've been watching footy for about four years now, and been a serious fan for about three.
And for the life of me, I still can not figure out the purpose of the body slams everyone throws in between play.

Honestly, what's the deal?  Everyone's walking back to position after a goal or behind or waiting for a ball-up and dudes are slamming each other.  You can see them make eye contact and line up for the hit.  No one gets hurt, it has no impact on the match, and no one gets in trouble.  And they all do it. 

And for every body slam, there are ten straight-up punches.

What's the point?  Do they just feel tough?  Does it show how dominant you are?  Is it some bizarre sign of respect?  Do the chicks dig it?

I just don't get it.