You can utilize this site in many ways. But it's particularly good for people who are new to Twitter and hoping to connect with quality local tweeps. This is because you can search Twopcharts by location and see who the top tweeps in each city are. Having found all the best local "influencers" you can decide whether you want to follow them or not. You can also check their lists of followers to find others to follow.
Because it's got a really straightforward interface, you can see the progress of certain people over several months and get a better idea about what they're like.
For example, I was checking out the top tweeps in Perth, where I live. I noticed that one of them had unfollowed heaps of people over a couple of months. Looking through his history I saw that this guy was using a churning method to beef up his follower numbers.
That is, he was following large numbers of people, so they would follow back, then dumping them when he had the chance. Not a good look in my opinion. And that made him someone to avoid.
Related ebook: How to Use Twitter to Grow Your Business.