Does a meaningful system always perform an energy conversion?

[Steffen Schwarze]

Using Lagrange and Hamiltonian mechanics we can describe a system as a
conversion between potential and kinetic energy. Does this cover all
meaningful systems? In other words, can there be a system, that has
for example moving parts, and does not convert any energy?

I think the conversion can be extended beyond kinetic and potential
energy. For example, a star is a system that performs energy
conversions (chemical, to mass, ...). It is also for sure a meaningful
system.

If there is "something going on", then for sure there is an energy
conversion being done, correct? For example, a gas cloud in space – a
simple system – but while it approaches a collapse into e.g. a star,
it does convert its potential energy.

Regards,
Steffen