Do you find it is a nessecity to tell people you are vegatarian/vegan?

Being a vegatarian for a year now iv basicly learned the do's and don't when it comes to eating on a vegatarian diet. First off I usally only bring it up if nessasary, such as if a friend wants to eat out and they dont know im a vegatarian. Also if i get asked quesions as to why i don't eat gluten, rennet or any types of meat i keep my answer short simple and respectful.