Commercial microwaves often don't have turntables. What they have - based on observation of a single one I took apart once - is a "scatter wheel" in the roof of the chamber, that spins just by air movement from the cooling fan, and reflects the microwave energy this way and that.
But that produces a stationary pattern (averaged over a rotation). Depending on where your food item is, some spot in it may never actually get high power energy if the overall scatter pattern is weak there. Actually rotating the food through a stationary pattern is likely to provide better coverage.
This is not proved. It is possible to set up an experiment to prove it. But it's reconciled me to the idea of the turntable. Also, consumer microwave turntables have, in my experience, been reliable.
But that produces a stationary pattern (averaged over a rotation). Depending on where your food item is, some spot in it may never actually get high power energy if the overall scatter pattern is weak there. Actually rotating the food through a stationary pattern is likely to provide better coverage.
This is not proved. It is possible to set up an experiment to prove it. But it's reconciled me to the idea of the turntable. Also, consumer microwave turntables have, in my experience, been reliable.