[ivanhoe]

Anything that you stashed just for convenience, but you could re-download or re-generate it if really needed, or simply live without it... frankly, like 90% of stuff on my disks fall in the category "I'll read/view it one day", which in reality I'll probably never have time or patience to open ever again.

[nixpulvis]

Strange, 90% of the things trapped in my flash memory are system files.

[vntok]

You should get another drive and reserve it to Data. The cost is negligible and it really makes everything much simpler.

Optimizing your system or upgrading it just becomes a "trash boot drive and reinstall" operation, applied without a care in the world.