Realy you dont need to delete the folders that are within the LAFFSV8 folder itself.. Just all the actual "files" that are contained in LAFFSV8 folder, That way no need to redownload maps etc.
Reason you need to delete stuff to start with is that I may have removed say 1 or 2 files, so if you dont delete them all and just overwrite them you still have the redundant ones left over that havent been changed and then you start to get problems with the UI....
But from my perspective its much easier to just say "Delete the entire contents" as I dunno what other stuff you may or may not have placed in there that may cause problems with an update
Hope that makes a bit more sense now...