A great many photographers only deliver your photos by way of a download. No disks, no thumb drives. Rest assured we DO include your photo on a thumb drive.
Anyway, you now have your photo files downloaded to your hard drive. Well, hard drives fail, computers crash. You don't want to lose your photos to a computer issue. We suggest picking up a few thumb drives, they're not expensive. Placing your photo on a 2 or 3 thumb drives or an external USB drive or two. Another suggestion is Amazon Drive, Dropbox, or other online services. In my mind, there is no such thing as too many backups.
I keep multiple backups on and offsite.