Page views, click-through rates, uniques, visits, conversions are old fashioned metrics. They are still widely used because most billing systems still rely on these metrics.
But let's say that you run a niche social network, and revenue is generated from advertising. The old-fashioned way to think: the more users, the more members, the more page views, and the more money you can make. This is true: all these metrics are proxies for revenue, as long as you filter out non human traffic in your statistics.
But what about finding better proxies, proxies that are more correlated with revenue? What about a more modern metric: weighted uniques. While uniques is the count of all distinct users visiting your website in a given time period, weighted uniques is a weighted sum where some users get a higher weight than others, reflecting the fact that not all uniques are created equal.
For instance, if your website caters to Americans, an US visitor should be assigned a higher weight than a European visitor. A member (a visitor who signed up) might get a higher weight than a non-member. A University student might get a higher weight than an older user because the lifetime value of a student might be higher.
This weighted metric, when used to drive business decisions, will have a better impact on ROI than the traditional non-weighted metric. In other words, increasing the weighted uniques will produce better results than increasing the non-weighted uniques. This happens because advertisers care about the quality of the traffic that they purchase, and they want uniques that convert and generate revenue.
Finally, the weighted uniques is also a better metric to assess the health or your business.