The water pan is (IMO) most useful for those learning the tricks and nuances of temperature control. Since water boils at 212°F it keeps temperature from going too much higher than that. OTOH if you want higher temps, water in the pan is not your friend. My recommendation is for new owners to follow the directions until they get the hang of things. If you have experience with a UDS this is not necessary.
I will note that Aaron Franklin uses a water pan in an offset in his videos and I am reluctant to suggest that I know better than him (because I don't!)