Why do dogs have whiskers and what purpose do they serve?
A dog's whiskers allow her to communicate and receive information. A dog's whiskers, or more correctly "vibrissae" are are long thick hairs growing from follicles on the dog's muzzle (a hair follicle is the part that produces hair.) They provide protection for a dog's muzzle while navigating around objects, allowing the dog to sense object and to protect it from injury to the eyes and collisions with objects.
Vibrissae can also detect vibrations and even changes in air currents. The three main uses are sensing pressure, sensing vibration and touch. You may have noticed touching your dog's whiskers causes them to blink, this is an automatic reaction to protect the eyes from branches, and other objects that could be a danger.
Your dogs brain is fascinating, and within the part that is dedicated to dealing with tactile information or touching, almost 40% of it is dedicated to the face, of that 40%, a large percentage is given to dealing with information from the the upper jaw, where of course most of the vibrissae are located.
It is not uncommon for dog groomers to trim vibrissae for aesthetic reasons, this is usually due to the lack of understanding of both groomers and owners as to how important they are to a dogs day to day life. There are studies that liken vibrissae to how a blind person would use a cane. Dogs that have had their vibrissae cut, will often move cautiously, especially in dim/low lit conditions, dogs with vibrissae will sense the changes is air around objects and will use this information to avoid contact with obstacles such as walls.
Dog whiskers are also used to sense the depth of space in front of their nose or muzzle, and allows them to know how far their mouth is from an object in front of them.