Gates can be life savers in a live situation, but you have to be careful when using them for recording. The problem with them is that they can sometimes be too slow, this is beacuse the trigger circuit has to wait till it hears a signal and only then does it open the gate, this means that sometimes you lose the first part of the sound.
Secondly, If you are trying to fix a leakage problem which is really bad it means that the level of background noise on the channel is going to be pretty close to the level of the instrument that you are recording, this means that you have to set the threshold pretty 'tight', that is, just below the level of the instument but just above the leakage, the problem here is that if the player is 'dynamic' and plays the occasional note a little softer, the gate won't open and you will miss the notes completely.
In recording situations it is more common to record the tracks 'as is', leakage and all, and then automate the mixer's ( or PC's ) 'mutes' later. Alternately on a PC you can open the tracks in a wave editor and clean them up.
