It's a good idea to always keep a backup of important files, no matter where they are stored. Only The best way to work with Zip disks, or any other removable disks for that matter, is to use them only for storage and not as the working copy. The hard drive provides faster access and is made to allow more frequent access than a Zip drive.
Zip disks aren' t made for frequent and repeated access like hard drives are.
On a Zip disk, the data is stored on a thin piece of plastic. Hard drives store files on metal disks and are therefore more durable. This also means you will have a backup on the Zip disk while you work. This will help if something goes wrong. You can do this in the Finder by using Erase Disk under the Special menu.