I've got to admit I'm still lugging full frame gear around. There are two draws for me: high dynamic range scenes and night sky photography.

The downside is the weight. As you go up in sensor size, lens elements get larger too - so heavier lenses. Every generation of crop sensors get more capable, and every year FF feels heavier, so I'll probably move in that direction eventually. Meanwhile I can do this (no tracker just a fast 20mm on a FF body):