Hehe, good answers here so far.
All jokes aside....to answer your question, in order of frequency:
1. Laminating prints (who knew?)
2. Mounting prints, mostly to ACM
3. Applying premask/application tape
4. As a roll holder when weeding long runs of decals
We have a 12 year old GBC Titan that we use every day, and a 1 year old Mimaki laminator that we got for free when we bought our printer. (Sadly, the brand new one sits in a corner sulking most of the time)
They're definitely overlooked/underappreciated pieces of equipment but are essential for a sign shop.
I wouldn't worry your laminator making you money - they only go along with what the printers are sending their way.