I don't like long or bulky valve stems, so I avoid things like quick connects and MAC valves and grip filters. I have a two-hose manifold so I can have an Iwata and a Badger hose side-by-side instead of using even an adapter fitting.
It's not actually necessary. It would cost me only a few seconds to swap hoses in addition to brushes. But it doesn't hurt anything either: work perfectly fine.
I do the same thing as GregStith! I use a regular coiled pneumatic tool hose instead of a copper coil, but same function: it acts as a pre-filter condenser. Works fantastically! Since my coil hose is clear, I can actually see all the water it's pulling from the air during operation.
I like side feed brushes because they typically have a shorter front end than their gravity or siphon equivalents. Makes fine freehand control a little more easy & intuitive. My favorite brush for painting small figures is my side-feed SOTAR in part for this reason. My micron SB sprays best, and my HP-CS is the most hassle-free, but between the nozzle cap shape and the ultra-short front, the SF-SOTAR is the most dexterous when dealing with the tightly spaced physical shapes on figures.
I've never understood the line-of-sight thing people often cite in favor of side feed, as I'm never sighting long the top of the airbrush, and can't picture that as natural position. Even with my HP-CS, my vision is never obscured, as I'm always looking at the tip from a downward offset angle anyway. I've also never understood the asymmetric balance thing people cite as a con of side-feed, as once an air line is hooked up, that dominates the balance feel, completely overriding the weight of the cup. Even with the super lightweight hoses I favor, the weight of a loaded side cup is almost undetectable once I've got the hose acting as a "keel" in my hand.
When I got my first side feed, I got some extra cups thinking it would make color switching and flushing simpler, but with time, my experience agrees with DaveG's. Switching cups actually makes the process much more complicated and messy. Best to keep a single cup on for the session, and flush and switch colors the same way you would with a gravity cup.