Sometimes, there are only three numbers that matter.
Stepping from Zero to One is when a componet is being introduced. Stepping from One to Zero is when a component is being elliminated. From these systems engineering processes, the latter is preferred, but the former is the reality. Still, these two processes are usually well defined, and are driven by functionality.
The Else is the realm of non-functional requirements, the gate through which scalability problems enter the scene. Even if Else is only 4. Tomorrow it may grow to 57.
The Else is where concurency becomes a problem. The Else is where one should decide which way to scale – up or sideways. The Else is when no one can speak for sure without referring to historical data. The Else is the 2 am call when all is down and nothing works because memory was upgraded, and cache miss ratio is in the sky