Has anyone ever erased everything from an EHD?

[bttrflygrl]

I'm doing a major re-org of my photos. I have two EHD's - one is current, the other was supposed to be a second backup, but it hasn't been updated in ages. Without going into a whole explanation, I need to "empty out" the second EHD so it can hold a bunch of files temporarily while I move things around, just to ensure that if I screw up I'll have it all backed up. So...

Is there anything I should know or be careful of when deleting everything from an EHD? Thanks!