I am currently installing PVC pipe to act as duct for my dust collector. There will be a central pipe down the length of my shop, with a few branches coming off for specific tools.
So far, I've hung some pipe and connected it together with PVC fittings. I had planned to get it all loosely fitted together, and then go back through and glue it together with PVC glue and primer. But as I've pushed a few fittings together, I started to question whether I need the glue. It occurs to me there are some advantages to leaving it only loosely connected. If I should ever have clog, it'll be a lot easier to unclog if I don't have to cut the pipe apart. Ditto if I ever want to add branches.
I'm using the thinner DWV pipe / ASTM D2729, if that matters. It's mostly 4" PVC, with one 3" run for some smaller tools.