Presumably so you don't know where it's been whilst in for "work" doing.Many many years ago my Boss at Yorkshire Water bought a brand new Ford Cosworth,at some point not long after it went in for something doing,We and the boss never saw it again!,written off by one of the Ford employees.
I guess a perk of the job to use someone else car whilst (supposedly) in the workshop.What happens in the event of damage or excessive mileage on the clock at collection?.