Hey Mark, the simple answer is that Delphix significantly increases the utilization of your existing infrastructure and instances. When that utilization goes through through the roof, you can capitalize in two ways:
You are able to get more out of what you paid for. (i.e. That 64 cpu ESX cluster under the RDBMS licence can now support 3x projects) [Same license, more benefit] or
You are able to shed excess capacity (i.e. Since you can now run all of your project databases on two ESX clusters, you can now use the other two for other purposes and don't need to be covered under your RDBMS license).
Obviously, the particulars all reside in how your license deal is structured with your RDBMS vendor (i.e. A ULA/ELA would not be impacted). Anyway you slice it, whatever you are paying today will return far more on the investment when coupled with Delphix.