We already know that a beard looks awesome and commands respect. There's a reason other mammals at the top of the food chain, such as lions, sport a pretty spectacular mane. But what are the actual benefits of a beard on a man, especially a warrior?
For starts, a beard offers protection. Protection against the elements, such as snow, rain, sand, and wind. Protection against bug bites and thus protection against diseases associated with many insects. Protection against bruises and cuts, which could otherwise expose the body to infection. Protection against the sun and damaging UV radiations as well. Beards even provide a barrier between allergens such as pollen and your airways, minimizing the incidence of asthma and allergic reactions. Beards also shield your neck from the cold, raise the temperature of your neck, and decrease the incidence of colds and coughs. Beards further protect against gum disease by filtering bacteria that enter the mouth. Beards even add an extra layer of protection between chemicals, fires, and heat, and your skin.
A beard also helps you heal better and faster, by knitting wounds and tears together like suture. A beard minimizes small cuts and potential skin rashes inherent to shaving, while reducing the use of water in the field. A beard also naturally keeps your skin moisturized. A beard further reduces acne, and thus, bacterial infection. A beard also includes beneficial bacteria that improve overall health and your immune system. A beard keeps you warm in cold climates by providing insulation, and cool in warm climates by wicking sweat from your face.
Throughout history, from the Norse to the Celts, beards have further conferred men prestige and authority, while allowing warriors to intimidate enemies. To this day, the Special Forces of most countries sport beards. Even the most bad ass Norse gods invariably have epic beards directly associated with their personification of masculinity ideals.
Furthermore, a beard signals to potential mates sexual maturity, and from an evolutionary perspective, bearded men are also perceived as tough, mature, aggressive, dominant and masculine. All characteristics highly desirable of a warrior.
Ultimately, a beard simply and effectively separates men from women.