In my opinion, if you do not have one attached to your account and something bad happens, Blizzard will usually work with you more if you add one after the fact and state that your account was hacked. This happened to me here with a leveling service and the guy cleared out my account completely. Blizzard returned all of my lost items/gold and asked me to add the authenticator to secure my account. I feel that if I would have had one they would not have done anything, as they would believe that I was somehow involved with what had happened since it would have been more unlikely that my account got hacked.
This post was edited by 3ironman on Dec 17 2018 10:23am