A new sound. Skillfully playing a four-finger roll can give you a completely new cadence to add to your picking repertoire, just as three-finger playing did in comparison to two-finger playing.
Speed. Not speed just for the sake of speed, but as an extra spice, if you will. Being able to play a really fast breakdown and being able to modify the cadence of your picking is something that will be readily apparent in your playing.
Versatility. With an increased repertoire of rolls at your disposal, you’ll be able to vary your breaks to a much larger extent. Think about going from 2-finger (such as in single-string style) to 3-finger Scruggs style. Now imagine adding another finger and you’ll open up even more avenues to explore with new rolls. Add that to your existing 2 and 3 finger techniques and you’ll have even more!
One big challenge I immediately saw upon donning a pick on my right ring finger was that everything I had always taught myself about keeping that ring finger down had to go. “Heresy!” I said. What if I want to play standard stuff with three fingers and just pop a quick 4-finger roll in there occasionally? I could, but I would have to keep that pick on for the whole song, which means I’d better get used to wearing it for any of a variety of picking situations: pull-offs, double pull-offs, Reno-style thumb brushes, up-the neck stuff, etc. Would that be worth it?
Another challenge is simply the newness of it. It really is starting over again, complete with the excruciating slowness of beginning anything for the first time. But I remind myself of the fastest banjo player I had ever seen (at the time). I never knew his name, or the band he was in. He was a banjo player on APT (Alabama Public Television) back in the late 70’s. He could play about 15 notes per second. But what was really inspiring about him was the fact that he had no thumb! Perhaps he had been in an accident, I don’t know – but he had learned to use his index finger to pick down and his middle and ring fingers to pick up. Simply amazing! If he could learn that, then I could learn anything, I have since told myself.
Also, does this mean you won’t be able to play three-finger style anymore, as your fingers will somehow not be able to do both? I don’t think so. I can play both Scruggs style and single string style without each interfering with the other, for instance. And so far, experience has validated this. As I improve with this new technique, I find that I can do it either with or without that 4th pick, keeping the ring finger down on the head when the time comes to do that.
One more challenge I’ll list here is that with four fingers, the number of possible rolls increases tremendously. I’m not sure how many of these are truly practical rolls, but I’m sure there are more variations than you have for 3 fingers.