For example, if you go to a popular blog that uses the system it will have lots of comments. You can then look at the profiles of those who made them and see what other sites sites they've added their thoughts to. So it's a great way to find related blogs that have the platform.
There are so many of them you'll never run out of new ones to find and engage with. You can spend your whole time in the world of Disqus. It's a little like Facebook in this regard, although it's not a "walled garden" like that site is. It's more of an extension of the blogosphere.
The other thing I like about it is that once you make comments they're all archived on the system and kept in the one place. So it's a bit like a separate blog comprised of all your comments on others.
This is a real bonus because when you comment on blogs normally it's very hard to keep track of which ones you did contribute to, as well as what you actually wrote. But on Disqus they're all there right in front of you. You can then use that content as the basis for longer articles and posts down the track if you wish.