The main advantage is that it frees up space so it looks better. It's also a lot quieter and if you get a good make it makes it easier to maintain and I have found you have to do it less often. People also say it leaves the tank water clearer. The media in my U4 needed rinsing out in dirty tank water) every week and I have done my eheim once since I've had it. It wasn't entirely pleasant but less time consuming in the long run.