I have nothing against cloud storage, in fact I use it for my final backup. But I'm averse to adding "one more subscription" to the massive amount my family is already paying for various subscription services, when I can manage everything locally, with relative ease.
Not to mention, most cloud services for photo storage mine those photos for facial recognition, building a massive database of faces and names to sell to data aggregators. I suspect Apple is one of the better services, in terms of data privacy, but I don't feel any burning need to start uploading all of my family photos. The cloud storage I use for final backup is run with local encryption, so it's protected in transit, and not even the cloud service themselves can decrypt the data.
If you're confused about "the cloud" in general, it just refers to the way data farms duplicate to multiple locations. When you upload your photos or phone backup to Apple's iCloud, that data gets copied to multiple sites, as a means of disaster recovery. If managed properly, the goal is zero loss due to natural disaster, war, etc. For more daily use, the multiple site model enhances speed, as you can always push/pull data to the site with which you have the closest connection, with it replicating to the other sites during off-peak hours.
If you have a NAS or any device with a RAID controller in your own home, then you already have redundancy built-in. I run newer, smarter variant of RAID-10, which ensures any data stored on any drive in the array is also duplicated on at least one other drive within the array. So, available storage is roughly half that of the sum of all disks in the array. Then that gets backed up to the cloud, with hundreds of available restore points going back several years. If I realize our children's baby photos have been deleted or corrupted three years ago, I can easily go back and retrieve an earlier copy from the cloud. More often, I'm relying on my local backup, hourly BTRFS snapshots, to retrieve a file I just accidentally deleted 5 minutes ago.