I just searched for mute groups and while a couple of threads came up, there was no real feature request for it, so here it is:
Mute Groups:
The possibility to link together two (or more) samples from the same (or different) instruments, such that they cut off each other when played (live, via midi-keyboard, not sequenced!). Think of a hi-hat on a drumset, when the open hi-hat is played, followed by a closed one, since this is the same cymbal, the open sound will be cut off by the closed one.
Such functionality is pretty common on all kinds of samplers, and necessary for recording sequences live.