Likely because there are people in the building an

Likely because there are people in the building and others who come by and want to come into the building. Also, they may have signed a long term contract to get a good rate. Possibly they are required to have a sign in/out for insurance purposes. It could also be a health and safety requirements from WCB. Maybe it's because it makes the neighbours feel more secure... I can do this all day lol