"Finally there are privacy issues, when systems are given to other users without creating new accounts. Mr. A lends its system to Mr B. Before doing so he moves away data on which he has signed NDAs or which is anyway private (e.g. bank details). Unfortunately, Mr B. finds bits of that data in the search database (e.g. a password)."
There are so many other ways for this to go wrong that I think it has to just count as bad practice anyway. For personal systems (e.g. laptops for employees) you will want to completely wipe them between users.