I worked for a dealership, so it might be different than a place that is open to the public. But it's not something I would ever do. I got backed up all the time because of it.

If things don't dry properly, they can mildew just like anything else. Mildew in rugs, they're easily replaced, but anywhere else in your car, it can be a problem.

In extreme cases, cars are junked just because mildew, mold, bacteria, basically anything organic got out of control. They can be fixed, but it costs more than most cars are worth.

I had to deal with those kind of cars a lot, so I would never risk it.