We only require a cleaning on move-out but we give our clients the option to require mid-stay cleans since that would be an additional expense for them. I know a lot of MTR operators swear by these mid-stay cleans but I haven't felt the need to require them.
No requirement on cleanings during the stay. This is something we offer the tenant if they want to elect to use the service for an additional fee. I have not had anyone choose to take this cleaning option. I go in and change the air filters either every 30 or 90 days depending on the filter type. This allows me to see the condition of the home and how they are treating it.
We've been doing once a week for our own sake, we just want eyes in the property to see if everything is still the way we left it (nothing broken/damaged, stolen, etc).