Personally, I only use an SSD drive as a system drive.
Music files are stored on one of the mechanical disks in my PC and are backed up incrementally to an external mechanical drive about once a month.
Pictures and documents are backed up to the cloud, in this case, Amazon Prime space.
Don’t really do much video, but would probably go external HDD if I did.
But that’s just me, I guess you have to find what’s right for you and that will likely differ for lots of folk…