A Great question,
Some patients need the extra opening of their lower jaw to lessen strain in the TMJ joint during sleeping hours , or to open the lower jaw to aid in sleep- apnea.  So wearing a night guard can be very beneficial , and you can easily have one made and fitted if you have some natural teeth remaining and wearing your partial, but if you have complete dentures, this may be not as easy because of the dentures possibly becoming dislodged during sleep.
Sometimes the initial cause for the need of a night guard may be the reduced vertical height of the dentures, having to make up the lack of proper height with a night guard.
First make sure your dentures and/or partials are of the correct height for you.  If they are , you may not need a night guard at all.
This also is an excellent and more frequently asked question that only after being examined by a properly trained practitioner who can diagnosis the correct height of your teeth , both natural and denture within your jaws, and should the dentures be replaced to a more correct vertical height or then a night guard be made and properly instructed in it’s wearing of.
Thank you,