Yes... Just one more data write. Just more wear on the drive.
I'm thinking of requesting that my rental clients NOT ZERO THE MEDIA, especially the RED-RAM and CF cards, which have a finite number of write cycles. And then I just handle testing and zeroing of the drive before it goes out on rental again.
I think most rental customers will prefer it this way. It takes a significant amount of time to erase a drive. Took me over 4 hours to zero the RED-RAM today in my testing with it connected to FW800.