A 'Choke Group' lets you specify samples that will cut each other off when triggered. The classic use for this is emulating a hi-hat 'choke': first assign an open hi-hat sample with long decay to a choke group, then assign a short closed hi-hat sample to the same choke group. Trigger the open-hat sample first, followed immediately by the closed-hat sample. You'll hear the open-hat sample cut off prematurely.
Although choke groups in drum machines were originally intended as a feature to make it easier for musicians to make more realistic hi-hat parts, it's useful for a ton of interesting effects. Experiment! Try assigning a long boomy kick drum sample and a short percussive kick sample to the same choke group.
Related Tasks:
Assigning a channel to a choke group