Everything you read, including my own postings, will tell you that iCloud is not backup and you shouldn't treat it as such. You should have multiple backups of any data you either don't want to lose or would be a bad use of your time to re-create. I say multiple because one is never enough. At least one on-site and one off-site is probably a minimum from my perspective.

So what of iCloud. It's a syncing service like DropBox etc and Apple themselves make zero guarantees that it won't lose your data, if there is a bug in their software or if you do something stupid they may throw their arms in the air and fail to recover your lost data.

It's incredibly handy though and can be used as a recovery vehicle. Got a new macBook? sign in to iCloud and restore your Desktop, Documents, Contacts, Photos, ToDo's, Notes, passwords. It's all there - or is if you turned it on.

I have given up on multiple attempts to fix my non-syncing Photos library. Today I started with a new empty library, turned on iCloud and went out for the day. Came home to 24K+ downloaded photos and videos. As far as I can tell everything is there. My Photos, albums, shared albums, labeled faces, keywords, everything. I should have done this two weeks ago.

Maybe iCloud is a backup service in some ways. You should still have backups but as a first port of call for restoring data, it is probably the one to go for.