I had an argument with a superior about this. Though at first glance the prior user of a laptop only did work in his own documents-folders, should I always install a new OS for the next user or is deleting the old profile enough? The software that is installed is mostly also needed by the next user.
I think an install is needed, but except my own argument of viruses and private data, what reasons are there for doing so?
At our company it is allowed to use the PC for e.g. private mail, on some PCs are even games installed. We have kinda mobile users, that are often on site at a customer, so I don't really blame them.
Also because of that we have a lot of local admins out there.
I know both the private use and the availability of local admin-accounts aren't good ideas, but that's how it was handled before I worked here and I can only change this once I am out of traineeship ;)
Edit: I think all of the answers posted are relevant, and I also know that a couple of the practices we have at my company aren't the best to begin with (local admin for too many people for example ;).
As of now, I think the most usable answer for a discussion would be the one from Ryder. Although the example he gave in his answer may be exaggerated, it has happened before that a former employee forgot private data. I recently found a retail copy of the game Runaway in a old laptop and we had a couple of cases of remaining private images, too.