If it's anything like RimPy it lets you organise mods without having to load into the game first. Super useful if you've got hundreds of mods and the game takes an hour to boot up.

It's for sorting mods in the correct load-order to avoid errors. You can also convert steam-mods to local mods to prevent them updating, if you wish.

Yup, for Ludeon or gog purchases p.e..