Moffitt system is pretty clever, there's a circle hook at the end of the line, and the flies are built on tubes that'll slide down the line. So, the fish mouths a softer, more realistic feeling fly, then hooks himself as he pulls away on the outside of the mouth with the circle hook.
The reason people claim its snagging is because its on the outside of the mouth, not the inside. The reason that reasonable people don't think its snagging is because it requires the fish to actually take the hook.
Centerpinning involves mega-long dead drifts. The reel just spins around a center pin spooling out line while the current drifts your offering. Eventually, you see the take, set the hook and turn the drag on the reel. The reason this gets a bad name is because its easy to dead drift your offering down an entire stream dominating the water.
I know Jay does pinning, and can probably explain it better. Not sure if anyone here has actually tried the Moffitt system, most are unsure what PA law has to say about it.