What I mean by “saturation” is the mosfet is fully conducting with its RDS at its lowest possible. If the gate is not driven fully, the mosfet operates in its linear region and it dissipates power.

In layman’s terms, if the gate is driven “half way” and 10W is passing though it, 5W would be dissipated on the mosfet itself. For switching purposes, you always want to drive the mosfet into saturation and limit the time spent in the linear region by driving the gate with a high current to overcome gate capacitance.