Why are Site Analytics and Traffic Sources numbers different?

There is a unique "filtering" process happening between Web Insights and Traffic Sources.

Web Insights defines a site visit session as 4 hours long, so if a visitor returns every 4 hours, you will have 6 visits for the day.

Traffic Sources defines a site session as 24 hours long. Using the same example as above, if a visitor returns every 4 hours, you will have 6 visits for the day in Web Insights, but only 1 visit in Traffic Sources. This is why you see a difference in numbers between Web Insights and Traffic Sources.

The reason we are using different site session times for site Web Insights and Traffic Sources is that each report is measuring a different goal.

Web Insights, among many other metrics, is focused on measuring the number of visits to your site.

Traffic Sources, on the other hand, is focused on measuring what sources are driving traffic to your website (this helps detail traffic sources and their interplay with campaigns).

Let's say that a visitor was driven to your site today from Google Adwords, this would appear as a Google Adwords source in Traffic Sources. Now let's say that later in the day the same visitor returned to your website via direct traffic (entering your website into their browser). Although they did come from direct traffic the second time, we know that the source was in fact Google Adwords that initially drove them to your site, and not direct traffic. Therefore, we will not assign a source visit to direct traffic from this second visit. Again, the intention of Traffic Sources is to measure what drove the visitor to your site (on a 24 hour timeline), and the intention of Web Insights is to measure the number of site visits (on a 4 hour timeline).