Almost every shop has a compressor. But few have a vacuum pump, which is little more than a compressor that runs backwards.
Why would you need a vacuum pump? Well, these days most of the materials commonly used in woodworking are veneered. And most of us buy these materials with the veneer already applied. That works out OK for most applications.
But there are many times when we need materials veneered with woods not commonly offered by suppliers or that have a thicker veneer than the incomprehensibly thin veneers typical of manufactured sheet goods. Buying a veneer press is an option but this can run into megabucks. Building one is a possibility but most shop built presses are mechanical and somewhat limiting in capability.
A vacuum press, on the other hand, can be put together for a few hundred bucks. And a vacuum press is virtually unlimited in it's potential capacity. A vacuum system can also be used to laminate shapes that would otherwise require more clamps than even the most dedicated clamp junkie would have on hand.
Vacuum is easy to use. Get everything into the bag, close it up, fire up the pump and walk away. It's amazing what atmospheric pressure will do.