The purpose of my 2 Melta/
PF tac squad is for BIG, BIG, BIG nasty things. I wound em twice (hopefully) with the Melta-gun, charge in there, and then use the Power Fist to take it down for good.
No As.Can as I don't have any modelled yet (Stupid 3rd edition Terminators
)
I use the Scouts as a free table quarter grabber, really. You'd be surprised at how many people just ignore a little five man squad hiding out in one of the free table quarters.