Desktop Analytics devices

In a large environment (100k devices), when connecting desktop analytics with configmgr, is the target collection supposed to be a portion (less than 20%) of the environment? Asking because when you do, you get a warning about the global pilot not being over 20% of the total devices.  So, is desktop analytics supposed to be used for only a fraction of the environment??  My thoughts were that you add the entire fleet and you also add child collections of the target collection and use those (or a group of those) as your deployment plans... (which include the Pilot phase btw).