Unfortunately a lot of engineers who do this don't appreciate that flash has limited write cycles, and the issues with upgrading non-reproducible systems down the line.
A lot of projects using Yocto are not even reproducible after a couple years because people forget to save `downloads` and `sstate-cache`, I might add.
That's a good point. You don't need sstate-cache, but you do need downloads/ if you want to protect yourself from 3rd party sources going offline. I'd recommend archiving that folder alongside any released versions.