SMs are responsible for much more than cues. They are the the glue that holds the whole production together from before the first rehearsal until after strike. They understand, interpret, support and execute the work of the designers, performers, and directors; create the schedules for the various crews and rehearsals and keep everyone on schedule; juggle house emergencies, prop emergencies, scenic emergiencies, costume emergencies, skipped pages during a performance; they run understudy rehearsals and put-ins, deal with various union issues and on and on. The cues are the least of it.