In the simplest terms, that means you stand to see a much wider range of game-changing add-ons.
Creators build their content using PC tools that aren't dissimilar from the ones that Bethesda used to make Fallout 4. But mods take things to another level, especially in the context of Fallout 4.
Mods as PC users think of them haven't ever been common on consoles.
If this is a new idea for you, that's okay.