You may come across a situation where your competition can try to hurt your business and send a gangster to your restaurant. His sabotage can lower ratings of your clients. Also, some of them may stop coming to your place.
Protection from situations like this one is expensive. You need to research "Security system". This unlocks cameras that you can later place in Architect mode.
Cameras should be placed in your restaurant. Thanks to them you can stop gangsters from sabotaging your business and avoid problems. The first place where you should place cameras is a room where your clients eat - this is the place where most sabotages occur.