Targeting mostly application performance, distributed systems have constantly increased in size and computing power of their resources. The power supply requirements of these systems have increased in a similar fashion, which has raised concerns about the energy they consume. This paper presents the Green Grid'5000 approach, a large-scale energy-sensing infrastructure with software components that allow users to precisely measure and understand the energy usage of their system. It also discusses a set of use-cases describing how an energy instrumented platform can be utilised by various categories of users, including administrators, Grid component designers, and distributed application end-users.