This plugin implements a modified version of the standard Memcache cache. Specifically it allows multiple, distributed, memcache stores to stay in sync with one another.
The most common use case for this is when using a load balancer, you can create memcache services on each front end server, which allows for very fast fetches. The tradeoff is that when updating the cache, the update will have to be performed against every front end server, which is comparatively slow. Some Moodle caches, such as Language Strings or Database Schema, have a very high number of fetches compared to sets, which makes them prime for this type of cache.