What is the purpose of toilets and cleaners?

Once you are level 8 or above, some customers will want to use a bathroom after eating their meal. These customers will not give you a thumbs up (to improve your popularity) until they have used the bathroom.

Therefore, if you do not have an available, clean toilet, the customer will leave with a toilet icon above their head, and will not increase your popularity. Hence, having enough toilets for your customer base assists your popularity.

A cleaner will be able to clean the toilets whenever they require cleaning, hence allowing your restaurant to continue running smoothly. In addition, they can clean up trash as well (this will add to your cash, gourmet points and towards your trash trophies, as if you cleaned the trash yourself). When there are no toilets or trash to clean, they will just generally act as though they are cleaning your restaurant, by scrubbing the floor, or similar.