Performance is an important subject when a project grows. There are some good practices that make projects more maintainable, like dependency injection, however, creating all the objects at the beginning of the request could reduce the application performance. If some of the created objects are not finally used, we have wasted CPU time and memory for no reason.
If we used proxies for every expensive dependency, the previous problem would be solved. We can still inject the dependency, but it will be wrapped by the proxy, which will create the object itself once we need it, or never, if it is not finally used. This is the principle behind lazy services. The ServiceManager makes use of the ocramius/proxy-manager package to create proxies on the fly for all the services configured as lazy.
He talks about the
lazy_services functionality the ServiceManager provides and gives an example of it in use defining a database (PDO) connection. He talks some about how it works behind the scenes and how no code change is required to use this new configuration.