It is not essentially required to get a gloss, as a two pack paint finish done well should have high gloss with minimal peel. However if you have imperfections like specs of dust, dry spots, runs or any other blemish in the top of the solid colour or clearcoat for metallics, then most of these imperfections can sucessfully be removed. Experience counts in these situations so the finish is not ruined and the job has to be redone.
Now also in regards to buffing two pack. If you are after a concourse or perfectly flat like a mirror paint finish, then a complete rub back and buff will achieve this finish. I have seen paint finishes off the gun that exceed the quality of most new cars, be fully rubbed back and buffed to a finish that exceeds most peoples ideas of car paint finish.
Just remember these types of finish take time. Hours = dollars.