When i was a kid, photos came in physical form, both as prints and as negatives. These could be stored in different locations, although most of the time they would be stored in the same location.
These days it's all digital photos, and i think most people agree that some kind of backup is needed. If you primarily use a cloud service, there is probably little risk that your data suddenly vanishes (though it has happened), but instead you're faced with the danger of losing access to that account, meaning your stuff might still exist, you just no longer have access to it.
My "normal" backup routing is simply "iCloud -> Mac Mini -> external harddrive + OneDrive", and the Raspberry Pi and Kopia is a (long running) test to eventually replace time machine.
As for the M-disc archive, it's a convenient and low cost way of creating resilient backups of my photos that doesn't require me to print everything. The archive will survive a lot more hardship than your average digital media, and does not require somewhat frequent usage to retain information. Harddrives lose their charge after 5-7 years of sitting unused, SSDs in as little as 2 years. Blu-Ray media will retain information for decades, and (according to the sales brochure) M-disc will retain information for a millenium, which i assume is about 900+ years longer than i need it to.
In theory, i could simply ditch the remote backup and rely on the M-disc media, but that's where convenience comes into play.
My photo library contains a large part of the moments of my life worth remembering, from being a kid, teenager, young adult, meeting my wife, our kids , pets, and everything between. I would seriously hate to lose it because somebody knocks over a can of soda.
There are two major threats to my photo library. One is loss of the cloud data
and/or loss of access to it (and/or malware, natural disasters, etc), which is why i keep data locally as well.
The other is loss of data locally, anything from a failed piece of equipment to a house fire.
The reason why i make a local backup of the synchronized cloud data is in case malware decides to encrypt/delete all my photos, in which case iCloud will happily synchronize all the changes to all devices, effectively deleting all good copies.
So with a local backup of the data i've mitigated the first threat, loss of cloud data and/or access to it, but i'm still left with the threat of losing data at home, which is why i also backup to a different cloud provider, which again comes with a threat of losing access, and this is where the Blu-Ray archive comes in.
Because burning Blu-Ray discs is time consuming, i rely on my "day to day" 3-2-1 backup to keep data safe, but ultimately the Blu-Ray discs safeguards against loss of cloud data and loss of local data (identical copies stored in different locations), so they're my last ditch defense of disaster recovery.
