plays only given % of ticks. so there are random pauses.
it is a very good excrcise.
i sometimes use slow (30bpm) and the tick is at the last 1/8 note. but that way i sort of "expect" or "wait" for the tick and the stuff i practice depends on it too much - gets monotonous. if the ticks are random (but in meter of course), those automatic expectations doesn't develop and independant thinking in time will improve.