I have been using a blowgun ever since I was 10, and I never used a mouthpiece on it. What is the point of the mouthpiece and do I really need it? What are the advantages and disadvantages of using a mouthpiece?
In short, they are not needed. Most people use them as they feel they are more comfortable to shoot with, provide a better seal, protect your teeth, etc. As a result, it is generally regarded that using a mouthpiece is a personal preference. I personally use a mouthpiece on my hunting blowguns, but do not use it on my target blowgun. If you are proficient without using a mouthpiece I would stick with that method.