I was wondering about this too?

If you're referring to what happens when you check in the "Parameter Mode Enable" box, then it's something that's been around for Max for Live for quite a while, and has now migrated into Max 6 generally. The Max for Live vignette that describes it is in the process of migrating to more Max 6-specific form even as I write.

The current vignette that describes them is "Device Parameters in Max for Live"

As ever, we appreciate your patience.