Before starting his work on his Carbon Backup app, Koush started researching into CyanDelta's updating system and decided to implement that feature into his own app. For those that don't know, a delta is created when the differences are taken between and old file and a new. CyanDelta would compare the nightly that the user was currently on with the most recently released nightly and it would download only the changes. This would allow for a quicker and smaller download, saving time and data.
Koush explains it on Google+:
Whenever a zip is requested to be downloaded by RM, the list of all other zips that were downloaded via RM are sent up to the delta server. The delta server then uses this to create an edge frequency graph (the actual CS term for this is slipping me at the moment), ie delta paths, from one zip to another. The edges (deltas) with the highest frequency are prioritized for delta creation on the server. If the delta fails, it will just fall back to full file. The whole process is pretty seamless/transparent.
Koush says that that the feature is still in beta, so watch out for bugs. Try it out and let us know what you think!
Update: Apparently I missed this yesterday, but Koush has also added support for for the Team Win Recovery Project! He says this feature is also in beta. Happy flashing!