Things are not simple when it comes to Software Eco-Design.

Eco-Design is about maximizing a software Efficiency function of Usage, which can be defined as a ratio :

Efficiency(U) = Utility(U) / Resources(U) (U = Usage, a parameter)

• Utility is related to the amount of useful work you can do in a unit of time (the word useful is important, because it depends on the context and what you need to achieve).
• Resources, for software is the amount of computation, data, I/O you use, which in turn, corresponds to an amount of energy (electricity) and hardware resources (servers, routers, wires, satellites, laptops, smartphones, …). The more software resources your application use, the more energy you will need, and the more powerful hardware you will use.
• Usage (U), corresponds of how your software is used. Usage is about how often your users will connect to the app, how many, from which county, etc. It is a parameter of Efficiency, Utility, and Resources because software impacts heavily depend on how the users will use it. The same software used differently may use up different amount of resources or have different utilities. Most importantly, Efficiency, Utility, and Resources might not be a linear function. Think of Amazon for instance: the utility might vary largely depending on the number of users, and the resources on where those users are located on the planet.
• Energy and hardware resources end up to be direct impacts on the planet, contributing to climate change or environment destruction (side note: the IT sector is expected to reach 10% of GES within 5 years, that is to say the equivalent of all personal vehicles worldwide).