What the register is actually for
It is for the situation nobody plans: an evacuation, an alarm, a fire brigade attendance, an incident where somebody needs to know whether the building is empty. In each of those the register is consulted and acted on. A cleaner who signed in and forgot to sign out has caused people to search a building for someone who left an hour ago, which is a genuine waste of emergency resources.
It also matters on shared industrial estates where several contractors attend after hours. Knowing that the cleaning crew was on site between six and nine, and that another contractor was there until eleven, resolves most questions about what happened to a door, an alarm or an area. Without accurate times, every question becomes an argument between parties who all believe they were careful. Accurate times turn a shared estate into something that can be reasoned about.
