I didn't have a proper footswitch for the drum machine, so turning it on or off mid-song could be a tricky proposition. (Changing beats was even trickier.) You would sort of stab at it with your foot or hand if available and hope for the best. Matching the downbeat to one's internal metronome could prove . . . interesting.
It's easier in some ways to play with a real live drummer, who often will provide visual cues (hand signals, the spinning drumstick) to the start and tempo. Or he could keel over as a result of a drug overdose, which would indicate that the song is probably not going to start in the near future. Either way, it puts an end to the guesswork.
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