Do not add water to the oils. The droplets of water will be too heavy to leave the diffuser. Unplug when not in use. Because heat is not used, the oils are not chemically changed or broken down. This makes nebulizers superb for clinical studies.
Nebulizers are incredibly efficient.
A much larger percentage of the essential oil is diffused. They will save you money by using less oils. Nebulizers are safe to leave unattended, and some have timed cycles or flow adjusting. This greatly expands the range of environments that they can be used in. Nebulizers can fill a much larger area than flame or electric heat diffusers.