I'm going to develop a script which use will be to aid the user on some tasks across pages which have in common a third party widget.
In order to do this I need this script to remeber things. Such things are alphanumeric data (strings) and possibily image files. This things must NOT be lost on browser's clear cache or browser reinstall possibily. But only by a TM's action supported by my script.
What's the best way to achive this with TM? I'd go with save/load into user's disk but I sense it could be troubled by security issues.
However, in case your profile gets corrupted there is nothing that Tampermonkey can do to preserve your data. Therefore you need to create backups. One way to achieve this is to backup your data via Options -> Utilities tab -> File/Zip Export. This will also backup the data stored via GM_setValue.
If you're using Chrome you can also backup your profile folder, because there are script to extract the data from such a backup: https://gist.github.com/derjanb/9f6c10168e63c3dc3cf0