I shoot three pin exactly as you describe, 20, 30, 40.
Will use an experience from yesterday to illustrate why I shoot 3 pin.
Had a doe come in on my off side. she was followed by two more mature doe and 2 young of the year. Any of the 3 mature were a viable target. At first it was the lead doe because she moved to a spot that I had previously ranged. With a single pin, I more than likely would have had it set to that distance.
The two young'uns were milling around below me, taking turns popping their heads up looking for danger, (which was very close to them).
The other two mature doe took turns turning broadside, quartering away, offering a good shot but then not. Had I been using a single pin, each time I changed primary targets, an adjustment to that sight would have had to have been made.
Now I am a "seasoned hunter" who has had a fair number of encounters with deer up close and personal. My number one thing to concentrate on when deer are near, is when to stand and draw my bow. You don't always see them coming until they are on top of you. I don't need one more thing to be thinking about at that moment.
However, with all of that said, my son switched to a single pin and has told me he feels it improved his shooting.
Think about your hunting situation, how comfortable you are in the moment, and decide what is right for you.
Good luck with your decision.
“I prefer my kid hunt and fish rather than steal and deal,”