What a diff having an air filter in the shop. I always turn it on when I'm in the shop and it just quietly works in the background keeping the dust down. I've found in my small shop that if I run it, I can then start finishing my projects, either spraying or wiping a finish on, with in 30 minutes of cutting or sanding with little to no dust ending up on the finish. I also don't have to worry as much about kicking up some dust from moving something or someone opening a door as I used to (helps that I keep the shop vacuumed now too).
I have a larger one that will do 1200 cfm, but I always run it on low so it's quiet and I use a double filter on the front.
Saves me lots of time from having to sand out the dust in between finishes.
So, if you run across one on cheap, jump on it, it's worth it just for the ability to do a better finish, especially on flat work.