I have a number of assorted 2.5-in SSDs & HDD doing various backup & archive duties, as well as sitting around idle.
Some irrational decisions had been made, such as using a 256 GB SSD for Time Machine backups of a system occupying 170 GB while a perfectly good 500 GB HDD that came out of a dead laptop was sitting idle.
Or backing up my disk image & compressed files archive to a 200 GB HDD with only 500 MB free space.
So I erased the 256 GB SSD & cloned the content of the 200 GB HDD onto it. Next I set up the 500 GB HDD as a replacement Time Machine backup for the 170 GB installation. There's a couple of HDDs, 200 & 250 GB sitting idle now. They may see use as Time Machine backups for a couple of G4 PowerBooks in my collection of older Macs.