IT technologies and products do not simply exist in a single state; rather they exist over a linear spectrum. Defining and standardizing the stages of this spectrum helps us more efficiently manage. We can anticipate and plan activities involved human and financial resources and prepare for changes in service.
This life cycle is frequently referred to in IT as SDLC, for System/Software Development Life Cycle.
Project management is particularly concerned about the upstream portion of the life cycle: determining requirements, procuring, designing, building and implementing. Operations management is generally concerned about the downstream part of the SDLC: running, optimizing, retiring, and replacing.
The earlier mistakes are caught in the upstream part of the life cycle, the less effect they have; likewise, the later mistakes are caught, the more effect they have downstream.
Below is a lifecycle diagram I have published and implemented in the past.