What does it all mean?

[vfromlmf]

A trade exception cannot be combined with a player for salary matching purposes. 

All I'm suggesting is the Mavs could waive Roby and then trade "air" e.g. something like a future 2nd for someone like Roberson + No 1. 

Roberson would fit into the Mavs TE and save OKC millions and millions. Probably not the best example, but that's the idea.

Another example might be Mavs future 2nd for Dion Waiters + No 1. 

A package of [ Lee + Jackson + MIA #1 + GSW #2 ] should get you a high level starter.

Mavs would also stay just below the tax line (I think)