The Quantcast tool is still relatively new – at least in comparison to SimilarWeb and SEMRush. Regardless, it offers high quality, relatively accurate traffic analyses. Although figures may not be exact, they are still absolutely on the right track. There are also advantages to having detailed information about the target group. An example of Quantcasts abilities:
Don’t panic, and take a step back to see the bigger picture. Perhaps customers are engaging with your website primarily on mobile rather than desktop. If your mobile site isn’t optimized or they are instead using your app, then this could be why. This gives you insight into how consumer behaviors change over time and where they are most likely to engage with your brand. - Preethy Vaidyanathan, Tapad
Another great way to get traffic is to join the social sites. They are popping up at an ever-increasing rate. By socializing with others on the net through these sites, everything you join or participate in gives you more people to see your site. And, if you're selling stuff from your site, you'll want to go to the places (interest groups) on the social site where people are interested in what you're selling.

Websites produce traffic rankings and statistics based on those people who access the sites while using their toolbars and other means of online measurements. The difficulty with this is that it does not look at the complete traffic picture for a site. Large sites usually hire the services of companies such as the Nielsen NetRatings or Quantcast, but their reports are available only by subscription.