Erase a back up external hard drive?

[Raven]

As a semi retired graphic designer, I use a
27” iMac with 2 EHDs as back ups. I use Super Duper and alternate the devices.
But over the years, the back up files/folders have been moved, duplicated, changed and some not needed anymore from old clients. I think my back-ups may be a bit of a mess.
So, any reason why I shouldn’t just erase one EHD and back up everything anew?
Then do the same with the other?

[Xairbusdriver]

I'd suggest waiting a couple of months between erasing the two drives. As one of the founding members has said, "Any time I have a fifty/fifty chance, 90% of the time I'm wrong"! If I had two backup drives, and erased both at the same time, within two days I'd find that one of those very old files (which is now deleted) was needed.

If those drives are over five years old, it might be better/safer to simply buy a new pair.

[Raven]

Makes sense. As usual! 
I’ll do one and wait a while for the next. Thanks!