Just as if you're downloading DLC or a complete game, it will show 'Space Engineers - Workshop Content' in your download list.If it's Multiplayer: MP is a different case, everytime you join a server it will redownload the mods used on that server as long you're not subscribed to those mods. But when a mod updates, the updated files will be downloaded from Steam's download manager.
Are we speaking about Single or Multiplayer?If it's Singleplayer: So far I know you don't redownload the mods everytime you load the world its just loading them from your workshop downloads.
