I have had a belt/disc combination in my shop for 35 or 40 years. And I use the belt at most 5% of the time. We are often a 2 or 3 man shop, and its really rare we find the belt our first choice. I freehand sharpen drill bits on the disc. I chuck a tungsten for tig welding in a cordless drill, and sharpen them on the disc. I debur a few hundred pieces a week- on the disc. I routinely round over the ends of round bar by spinning em at an angle, on the disc. I like the ability of the disc to flatten wider pieces (12" disc) than the 6" belt.
two things influence me in this-
its really easy to cut a rip into a belt, and destroy it in seconds, with a sharp piece of metal- whereas a 12" disc can get snagged, and you just move over a bit, and keep sanding.
and- 2- I buy really good abrasives. For both, I run the cloth backed blue alumina zirconia abrasives from klingspor, and it will just eat metal as you feed it in. Lasts a long time, although, always longer on the disc.
The friends of mine who love their belt sanders the most are knifemakers. Which makes sense. But for a general fab shop, we much prefer discs.