Webtrends Analytics 9 Adminstration Guide, November 2012
If you use Webtrends query parameters to track online marketing campaigns, you can use Visitor History to associate visitor activity to campaigns viewed in a previous visit. You can also specify how long your reports credit activity to each campaign, so that reports always show the most campaign-relevant data.
With campaign visitor history, you have the data you need to optimize your online campaigns.
As a best practice, you should only use campaign visitor measures in reports that contain one dimension based on most recent campaigns stored in Visitor History. You can also use campaign visitor measures in reports that contain two dimensions if both dimensions are based on most recent campaigns.
Do not use campaign visitor measures with dimensions that are not based on Visitor History.