Weight is probably more important overall, but size can make or break usability in specific situations. A 16” laptop is not fun to try to use in an economy airplane seat for example, but a 12”/13” (especially if it has a trackpoint to cut down necessary arm movement) works great in the same circumstance.
Weight doesn't really matter with modern laptops. They are almost universally lightweight.
I'm from a generation that walked to the school with a backpack full of books. I also enjoy hiking, which often involves carrying a backpack much heavier than your typical office backpack. When I take my office backpack, I have to double-check that the 16" MBP is there, because I can't tell it reliably from the weight. While I prefer small backpacks and avoid carrying unnecessary stuff, the laptop just doesn't contribute that much to the weight.
Physical dimension, on the other hand, matter. A 16" laptop can be inconvenient in tight spaces such as train/plane seats.
> Laptop size doesn't matter. Laptop weight is what matters.
Depends what you do with them. For years I have used laptops in development simply to avoid all the wiring associated with desktops, and for doing things like running the JetBrains tools, screensize and CPU does matter.
I don't do dev anymore, so my priorities have changed.