I usually toss it unless it's the only option. I did have a heel on one side of a salami sandwich the other day and shredded cheese since we were out of slices. Desperate times call for desperate measures.
Depends on the bread. TBH: Most American store-bought bread isn't very good, IMO. Something I never knew until I went to Europe the first time and experienced truly good bread. Soft, yet firm on the inside, nice and crusty crust. Crust that goes *crunch* when you bite it. Mmmm...
The end pieces, "heels," of such bread are the best.
It can be found here in the U.S., but you have to look for it and it can often be slim pickings.