Degassing mead is important, but may not be necessary. When you degas mead you reduce Co2 and introduce more oxygen into the must. Fermentation can get stuck or produce off flavors with mead, so degassing can fix this. You should degas during primary either every day, or every few days.

Is degassing mead necessary?

The purpose of degassing in wine or mead is to benefit the yeast. CO2 is toxic to yeast and inhibits the yeast's ability to fully ferment the larger amount of sugars in wine/mead. Degassing mead is highly recommended during primary fermentation to help the yeast, even if you plan on making a sparkling mead.

Should you Degas mead before bottling?

The mead should be degassed along the way of fermentation, which tends to help fermentation along. In this case, though yes you want to degas before bottling. I'd recommend degassing in the primary unless you are sure your fermentation is done (gravity check).