I will give you a little hint at the end of this, gating works good for instance if you have not sampled a clean 1 shot hit from a record or other source sometimes, that may either have some background effect etc that you do not want...since I am a drummer I can tell you that gating drums started in studio recording of drummers, sometimes kicks and snares in a studio have a very long decay and create untuned harmonics you might not want in the recording so a gate is used to cut it off...another approach that is an alternative to gating is I process samples in soundforge that either I do not want a long decay or maybe that contain a background instrument and I cannot find a clean 1 shot on the record, I use an envelope on it , I have being using envelopes on my drums for awhile if you mess around with it enough you can lift a snare or kick out of a mix that you would normally not use......