Depends on your bass and playing style. Not just to be annoyingly vague, but it really does! You need to have the 'door' or decay set just right so that it allows the trailing end of the note to pass through but starts to shut when the hiss overtakes the bass sound for volume. To me, 20% is about right (I use it on my Musicman Vbass patch but the thresh is at 37% - but then I play very lightly)
To be honest if you use it sparingly it should not be noticeable at all in the mix when listened to solo - and it will be very hard to detect in the context of a mix or live song. Just be careful that the threshold isn't too high and the decay too low otherwise you will hear a distorting of the decaying note as the door slams shut and cuts it short - again, an interesting effect for driving synths and so on.
If you are getting lots of hiss without the gate switched on you might want to see if the problem can be solved before it hits the pod. I get no hiss in the studio or live but do use the gate at home because of very light hum produced from my TV and so on which is picked up especially on the fretless which is usually played with the bridge single coil on full!
Hope this helps
ped