Question about linking 3ds and wiiu IDs

Obviously I want to do it, but I'm curious as to what is lost. Do you lose friends on one side? Do you lose one of your Miis? Anybody care to explain?

You don't lose anything. You can choose whether to use your WiiU Mii or keep your 3DS Mii on the 3DS. The 3DS friends list is unaffected, as it isn't integrated into the 3DS Miiverse yet. Nothing is changed on the WiiU side.