I would consider a piston upper for use in harsh enviroments, or really high round count shooting (multiple beta mag dumps or heavy full auto use)
But I really don't forsee any situations that I'd encounter the need. Hard to even justify it if the proverbial shtf.
Assumption is the mother of all ****ups.
Know what you know, Know what you don't know. -Paul Pedzolt
"Jack of all trades, master of none, though oftentimes better than master of one" -Mynshul