Do I need iCloud for my Apple devices?

You get 5Gb of iCloud for free. It is not required you use it or purchase more. You do want to make sure you are backing up your data in some way, including your photos, and iCloud does make that seamless The more data you have the more iCloud space you will need. The alternative to using iCloud for a backup is to backup to a computer. Without any sort of backup, your data will be lost when catastrophe strikes or if you forget your Passcode (or locked out by accident due to too many failed attempts).

Back up iPhone - Apple Support

The other benefit of iCloud is when you have multiple devices using the same Apple Account, so the data can be synced across the devices. Without multiple devices, that is not much of a benefit. Don't ignore the importance of a backup though.

The only way to mark data as being valuable is with backups.

Do you have backups?

If not, you’re one drop, one dunk, one fire, one failure, one loss, one theft away from data loss.

iCloud is one way to keep a backup.