In my opinion, all the posts above here are true and as correct as can be! I actually have an old Bonanza press from back in the 40's sometime that belonged to my dad. I learned to reload on it myself.
But with the progressive press discussion, I have seen many people discuss them like "progressive" is the only thing they do! I have a Dillon 550b, and have NEVER used it progressively. I use it like 4 single stage presses at times, and as a single stage most of the time.
For instance, the sizing die can be installed only. Brass inserted at position #1, are sized, de capped and primed. As another is loaded, the finished pieces work themselves out the other end.
Then if you get into forming brass for odd calibers from parent cases, four dies can be added, one to each station to partially expand or reduce the brass from one stage to another.
I think the progressive press has so many varied uses. And as I said I have never used it for progressive volume loading. It's too easy to make a mistake, or have a powder metering malfunction. I simply don't trust the progressive operation with anyones press.