If you subscribe to the premium content, which means you pay the monthly fee with crunchyroll, then you'll get episodes of stuff like Bleach and Naruto, etc. that you can't get with the free version that you normally get. You'll notice that you can already receive Bleach and Naruto, but you can't get the first few seasons of episodes, or can't watch them anyway, without the premium account. That's what linking will do. It also allows you to watch the more mature content because you've verified your age with Crunchyroll by signing up. That's about it as far as I know.