When assessing the contents of RAM in a typical running PC, many parts of memory have the same content. The redundant copies of data across system RAM present an opportunity to reduce the memory footprint even for services and OS components.
Memory combining is a technique in which Windows efficiently assesses the content of system RAM during normal activity and locates duplicate content across all system memory. Windows will then free up duplicates and keep a single copy. If the application tries to write to the memory in future, Windows will give it a private copy. All of this happens under the covers in the memory manager, with no impact on applications. This approach can liberate 10s to 100s of MBs of memory (depending on how many applications are running concurrently).