Whiskers are a very important part of any cat. They provide the cat with a sense of direction, stability, balance and location. It is imperative that cats have their whiskers at full length. Cutting cats' whiskers can be disastrous in the results. Don't do it - that's the general recommendation.
Having long whiskers is particularly useful when judging distances in confined spaces, the longer they are the less likely your cat is to bump into things. Whiskers sometimes fall off over time, but that is normal if it naturally comes off. If a cat is losing fur its whiskers can also go off.
Whiskers are also a way for cats to express their moods
E.G When a cat is calm and content, the whiskers are more relaxed and lose, as opposed to when a cat is agitated, the whiskers get tense and pushed to the back. When a cat hunts its whiskers shoot forward to detect the Prey's movements.