To the OP's questions. Does weight really matter? Matter to what? efficiency, speed, or for enjoyment?

I wish I had taken physics in school. The efficiency discussion above is interesting yet confusing to me. I guess what matters to me is having the right bikes for the right applications regardless of their weight is what makes it all fun. I'm no weight weenie, but I'll admit that I don't want my bikes to be heavier than they need to be.

I have just as much fun riding my 17lb CF road bike 100 miles as I do my on 35lb Fat bike riding 10 miles in the snow or dirt. It's fun to be able to load 20 lbs of groceries and a couple of growlers on my Commuter bike and get them home. It's fun to cruise around the hood on my old 40lb Schwinn speedster, It's fun to mountain bike on a 25lb hardtail. They all do what they do really well, and it's all pedaling which is what I like.

I have a dedicated commuter bike but, I can and have commuted on all of my bikes. Some go a lot faster than others, but I enjoy them all for what they are.