At runtime, a script sets up everything that it requires, allocating memory for variables and objects and all these gets torn down upon end of execution. There is no persistency beyond the notion of a session. [...] So, there will be lots of object construction and destruction going on while the user of a PHP web app goes about her business dealing with the same app. Here's where object caching with memcached helps.

He suggests using memcache to cache and retrieve objects as they're needed instead of creating multiples over and over again. It almost functions as a Singleton, checking to see if there's already an object created before sending out a new one.