Nothing except for the limited size. I believe even today, nothing exists today for temp storage that have the convenience of diskettes.

USB Flash Drives comes close, but cheaper versions can in rare cases have firmware “virises”. On a diskette, just do a format and all issues gone. Also I never even thought twice about mailing a file on a diskette expecting to never see that diskette again. Flash Drives, I still would like to get it back after mailing it out :)