Many many years ago 1 of my friend told me this situation, imagine u use SSD for downloading files / torrenting so hardcore like almost 24/7, the SSD lifespan will reduce drastically.

As some already mentioned before, don't just have 1 back source for important files, make it 2, or even 3 or 4 if u can afford it. Nowadays storage devices are some what cheap/reasonably priced. So having mechanical HDD for backup storage of any kind of files will be better than using SSD as the backup.

Imo, SSD should be used as the primary storage for OS and programs/applications that need faster read/write/ For backup storage purpose, having multiple internal and external hard disk (big or small size doesn't matter, storage capacity is up to ur usage behavior and requirements) will be a life safer for future.

Whether u want to use RAID or not, it also depends on how u want to manage ur backup.