I agree that it should generally not be mandatory, especially in the early game where options are limited. I could however imagine certain characters, maybe certain classes, having a sex need. As for the micromanaging, each slave could get a sex schedule, or just an option to automatically take care of sex needs. Slaves that like each others could be paired (or threesomed, or foursomed) so they take their breaks together, and the master's interaction is only necessary when you want particular pairings. Making sex micromanaging mandatory would obviously be bad, but sex, in a game largely about sex, should be more relevant; and it should have more far-reaching effects that are not limited to sex itself.
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A simple schedule, as in an option on every slave to automatically have sex whenever their lust is too high, with additional options to pick either the highest lust slaves as partner, their favorite slave, or let the master decide. You can decide to punish slaves by denying them sex, or make them serve others. Slaves assigned to the Service job will join any open sex slot to increase the enjoyment of other slaves; they will not enjoy the sex itself, but some classes decrease the tiredness gained from the Service job.