It provides a Damage Resistance of 2 as well as bonuses of 1 to Charisma and 2 to Small Guns. Only merchants can repair it; there is no other clothing with which it can be repaired.
If you sided with Tenpenny during the Tenpenny Tower quest, there is still a way to obtain his suit non-violently. Wait until he has started sleeping, then reverse pickpocket any clothing with a damage resistance greater than two into his inventory. Exit the interior map cell, and return to find him wearing it. The Lone Wanderer may then pickpocket Tenpenny's suit from him (this only works if the clothing given to him is in good condition and has a better armor rating than his own).
If you have done the quest Tenpenny Tower and helped the ghouls to get into the Tower, Tenpenny will be dead after a certain amount of time.