Casual use and booked use are different problems
Casual daily use of a terrace produces the ordinary load any outdoor common area receives: litter, leaf matter, marks on furniture and the effects of weather. A booked function produces something else entirely, concentrated into a few hours and usually finishing late. The two need different responses, and a single routine frequency will either be excessive for ordinary days or inadequate after an event. Neither situation is well served by a single fixed interval.
Separating them is the sensible structure. A routine cycle covers the ordinary condition, and a recovery attendance is triggered by a booking. That way the scheme is not funding event-level attention every week, and it is not left with a terrace in poor condition on a Monday morning because the routine visit is not due until Thursday. It also gives the booking process something concrete to attach a condition to.
