I'd say I draw from scratch probably 80% of the time. I wish I could get that down to about 50%, but I wouldn't ever sacrifice the story or a composition just because I thought I might be able to reuse some previous art.
I guess if your purpose is to learn to draw then reusing previous work defeats that, but if your goal is to pump out content, I advocate for reusing as much art as is feasible, without it become stale.
Sometimes I see people redraw intricate backgrounds from the exact same position and to me that's an indicator of OCD or something like that. All I can think of when I see that kind of thing is about how I'll be lying on my deathbed someday wishing I hadn't wasted all that time redrawing what I'd already drawn.