Hi soundfulslumber,
I think a mattress protector is an important part of a sleeping system. It can help protect the mattress from accidents and the moisture and body fluids that we all emit each night. It can also protect the mattress against the accumulation of dust mites (which feed on the skin particles we lose each night). It’s also much easier to remove and clean a mattress protector to keep your sleeping surface clean and hygienic than removing and cleaning a mattress cover and even a small stain on a mattress cover can void your warranty.
There are different types of mattress protectors though which each have their own pros and cons that you can read about in post #89 here. The thinner “membrane type” of protector are a very common choice because of their lower cost, relatively small effect on the “feel” of the mattress, and because they are waterproof although they can affect the sleeping temperature of a mattress for some people because they don’t breathe and ventilate as well as the other types of mattress protectors.
Phoenix