So I'm planning on doing a fresh install of Skyrim on Steam and make a new character, and I was wondering if the DLCs actually change anything in the game and/or game files other than the files that can be ticked off in the launcher(for example: Dawnguard).

Does each of the DLCs actually exists only in a single file? or does it also change other files and/or add other files?

This might be an elementary question but I'm just curious to how this works. I'm not really planning on starting any of the DLCs until very later in the game(possibly tens of hours in) so I think I'd tick them off anyway but either way it wouldn't hurt to know.

I own the Legendary Edition of Skyrim on Steam.