It does introduce a thing that I have to remember to do, and if I forget, it fails to work without warning (if the memory card fills up). This is no good for a device that sits there functioning for months and months and you never look at the output from it until one day you desperately need it.

This is similar to computer backups. You go through the motions every day for years, and one day you really, really need the output. If it turns out it hasn't been working for some reason, you're screwed.