Usernames and t.me
Official telegram.org Source
You don't have to get one. Remember that Telegram usernames are public and choosing a username on Telegram makes it possible for people to find you in global search and send you messages even if they don't have your number. If you are not comfortable with this, we advise against setting up a username.
Official Telegram Reference: https://telegram.org/faq
Part of the TGWAY.com Official Telegram Knowledge Base (98 Verified Q&As).