The drier, the worse off you'll be. If the enclosure is very dry any air movement will whip up tiny particles of roach frass etc from inside the enclosure, and inhaling these will result in a not-so-very-fun time for you! When the humidity is high these particles are either matted down on each other due to the moisture or held together by the intermolecular attractive forces in the water. This keeps them out of the air which is good for you! Add springtails, which consume little bits of food and fungal spores and you've got a natural combination for keeping things clean and non-irritating. The cleaner beetles (probably lesser mealworm beetles) are great for eating larger debris (like dead roaches) but if you have a lot of grain products for them to munch on in your container they'll eat those instead and their waste will contribute to the cleanliness problem.