I've read through numerous forum posts that discuss using only ganache coating under fondant with a buttercream filling.  Is there a good reason to only use ganache to dam to prevent the BC bulge but fill and crumb coat with buttercream before putting on the fondant?   

I will often just use SMBC as my dam and filling before fondanting. I make sure my cake is cold, my SMBC is nice and firm (still spreadable/pipeable, but just not warm and sloppy) and then once the SMBC hits the cold cake it firms up even more making it nice and easy to stack and squish the air out as I go. Then it's into the fridge again (I usually try to time things so it can have overnight in the fridge to really settle and firm up) and then on with the fondant. Hope that helps  x

I don't think I've ever heard of a ganache dam? I do it like meme1 does --

I've heard of it, maybe it is used in hot climates, bit I sure don't want to bite into a big glob of chocolate in the middle of my cake.  I always use buttrcream for my dams.

but whipped ganache yes but not the liquidy stuff