For my first few years of building calls I poopoo'd the idea of using a reamer on my barrels. I was getting by fine without one. I pin most of my bands, and my pinning jig is based off of a very precise 5/8" hardened steel shaft. After drilling a lot of barrels, it was pretty unlikely that the true 5/8" shaft would fit through the 5/8" hole cleanly, so I was having to sand a lot to get it to fit. The reamer fixes that little issue perfectly. Mine is a chucking reamer and has a round shaft, so I just have it mounted in my bench vise most of the time. It is very easy to run a drilled blank over it and clean it up. It is amazing how much wood it removes. I chose a spiral reamer, which cuts very cleanly and easily. My reamer is some of the best $50 I ever spent.
I also use a spiral tapered reamer in my duck calls' exhaust after step drilling. I mount it in the Jacobs chuck on the lathe and run it in there after all my drilling is done.