This option is so ease, it's scary. Once you select Facebook Page option, you'll be asked to login into Facebook. After a successful login, you'll be presented with a list of Facebook Pages where you have administrator access. Select the one you want and Webtrends will do the rest.
You now have access to all your Facebook Insights data in a much more user friendly presentation. As an added bonus, you can now grant other Webtrends users access to this data. Normally your require administrator rights to the Facebook page as requirement to see the Insights data.
Because Webtrends uses the Facebook API, data tends to lag 2 days behind the current date. I've seen it lag more than a 2.5 days behind, but that's not Webtrends fault.
If you have the Facebook Analytics module from Webtrends, you can capture additional data but for most part for small to medium sized business simply having this data all in one spot may be all they need.