Exhaust Routing???

I've noticed that some of the guys running around here have their exhaust pipes run under the gas tank...I haven't ever thought about it before, but what are the advantages/disadvantages of these setups??? And which companies make their catbacks like that??? It seems that it would greatly reduce ground clearance, but it allows for a bigger pipe and less power loss over the huge bends...any opinions???
 
actually...these setups have been on GT's...it is possible they've had IRS swaps, but I've seen it on multiple gt's in the last year...I'll try to find a pic and add it to this post...

edit...found a picture and you're right 'silverbullet00'....the red mustang on the 1st page of the pics thread has what I'm talking about 'dew22'...and it shows in his mods that he has an IRS swap in the rear

thanks for the reply