As with all things, suppressors on their own don't do anything.
With that being said, I believe that an AEG with a perfectly shimmed gearbox with a spot on motor height and the correct air volume ratio for the bb weight used will benefit a lot from a suppressor, provided it's well built.
This from the target's perspective, I've been on the receiving end of a couple of guns that were really well built and I could barely locate the general direction of the incoming fire. On full auto, due to the longer lasting sound report, you can easily pinpoint it even if it's super quiet, but in semi? the shooter has way more chances to not be spotted.
Oh, obviously a suppressor on a Fire Hawk makes no sense other than cosmetics..
The fart flap Adolf mentioned works really well in overvolumed builds, the excess air slips past the BB and opens the flap, which automatically closes as soon as the pressure drops (right after the bb has gone past it). Various methods to do one, most people simply tape the end of the suppressor and keep firing until BBs tear through it.