NEC Articles 350.10 and 356.10 both use the language "Where conditions...require flexibility or protection of liquids..."

In common practice, is this interpreted as only device which need to move or vibrate are allowed to be connected with flexible conduit, instead of rigid or thin-walled conduit?

Or is it allowed more liberally, that saving labor and difficulty is a good enough justification to use flexible conduit to connect devices?

Thanks for any insight,

Evan

348.10 FMC does not speak specifically to being used in situations requiring flexibility. Therefore it is allowed to be connected to equipment that does not necessarily move or vibrate. From that, I would conclude that LFMC, although designed to withstand some movement and vibration, does not require such an environment for it's use.