Nobody has noticed (or if they have, they haven't commented) that I've copy-pasted the inks from backgrounds I've drawn earlier and just edited them to fit the panel I'm drawing on multiple occasions in Errant. I also regularly copy-paste Excalibur because it's such a pain to draw.
If it allows me to keep an update schedule, put in more time on those all-important character drawings and save stress, I'll do it.
I draw the line at reusing drawings of characters though. I always draw them from scratch unless I deliberately want panels to look identical or almost identical for a joke, reaction or similar, because I like to have an organic, lively feel to my comic. That said, in some styles and certain comics can make it work. I'm a homestuck fan, and that comic reuses assets a LOT, often to comedic effect, but it's also just part of the aesthetic.
Basically, do what works for you.