yes, this seems sensible. i would definitely include cache by default though.

Hi! I don't mean to argue, just curious: what app's cache you appreciate so
high?

i don't particularly like caches :) but the point is that backups should reflect the state of that which is backed up. restoring should as accurately as possible restore how the package was when it was backed up, not create a somewhat similar state for it (unless the user wants that).
i imagine it could be bothering not to have the cache backed up on some media players if they store metadata or thumbnails there.
i think it's a flaw that abd backup doesn't do this if there is no way to turn it on (which i haven't looked into).
so i think it's a good suggestion but it should be opt-in.

Automatic cache management

Developer: #109 (comment)

Automatically clearing cache before backing up would massively help users as apps such as Firefox collect hundreds of megabytes cache (Firefox app size is ~ 50 MB) and clearing temporary files before doing a backup can make the process dozens of times faster for certain applications, based on my experience.
Giving an option to exclude cache is enough. TWRP doesn't back up cache by default, though.

Was this ever implemented ?

Would it be possible to at the very least make cache backup optional? Certain apps like FDroid store large quantities of data in cache that nobody would ever want to back up.

I just tested it out with a mere 30 apps, and clearing the cache removed almost 300MB (after compression and encryption!) of useless data from my backup folder.

Firefox seems to persistently store 600 MB of cache on my system (OnePlus One, 64 GB).