For quite a while, my "laptop" was essentially a desktop that I could take home with me. It went into a dock on my desk at work, it went in my car, it say on a desk at home. I didn't travel very often, so its weight and battery life were pretty irrelevant. The kids also had laptops, which were essentially small desktops that they could take to their rooms. Ditto.
Then the kids went off to college, and they wanted something they could take notes on in class, carry around campus in their backpacks, and use between classes wherever they happened to be. Size and weight became relevant. Battery life became important. There was one of those "ultrabooks" (12inch screen, smaller than a textbook) on sale at the time, and I bought one for my son. It was ... rather nice. I bought another one for myself, and started using it when I did travel, and it was a LOT nicer to lug through airports (especially since airlines cut back on free luggage, so most of the time you'd be lugging a carryon suitcase and a laptop bag all around.) I preferred it a lot, for anytime I didn't actually need "big computing power."
(I now have a "gaming laptop" as well. It's ... hilarious. I think just the power brick for it weighs more than the ultrabook INCLUDING it's power supply.)
For the people who really need laptops, small and light is nice. ("at home", you can connect it to a full-sized keyboard and display, right?) If it's just a "luggable", then you can go for the bigger and heavier machine.