My attempt at a helpful answer:
I think there's some confusion about the term "break in". Some people define it to strictly mean the use of specialized "break-in" color slides viewed for a set number of hours before normal use of the panel can commence. Others use the term to mean a period of time - roughly the first 100-300 hours - where the user should be cautious about the content he/she watches, paying careful attention to avoid static logos and game HUDS for extended periods of time, to watch as little letterboxed/pillarboxed content as possible, and to reduce contrast on the set.
If your definition is the first one, the answer to the OP's question is a resounding NO. Break-in slides are not necessary. You may hear mention on this forum of special slides provided by the user D-Nice for certain sets. These are NOT break-in slides, but rather are used to get your panel exactly where D-Nice's was when he began his calibration. They're only for people who want to try his settings, and have absolutely nothing to do with IR prevention.
If your definition is the second one, then the answer is: "it's advisable, but probably not necessary." It sort of depends on how cautious you want to be. Personally, I'm being cautious with my ST60. I'm still within the first 100 hours, so I'm limiting static logos and black bars, and I turn down the contrast whenever I'm on a channel with static logos. But that's me. Deep down I know that I could probably be paying it no mind whatsoever and never see a bit of IR.
Some people say "better safe than sorry", others watch their TVs normally without a second thought. The bottom line is that even if you DID see some IR, it's just that: image retention, not burn-in. In other words, it's temporary.
Do what feels right to you and enjoy your TV.