I'll throw my two cents in the ring...and my opinion is probably worth just that.
I can agree with both sides of the conversation on this one.
IMHO, there will NEVER be any damage to your butt no matter if you break with it or not. You do run a chance of "exploding" your shaft depending on the joint, however, the odds on that are minimum. Again, this is just my opinion.
Regardless if you use a break cue or not you are always going to be faced with premature mushroom if your using a traditional leather tip.
The talk of joint damage because of the unneeded threading and unthreading of the shaft makes me think of numbers.
In a race to 9, you will never break more than 9 times. Regardless if it's a winner breaks match or not. Win or lose, 9 is the maximum number of times you will break the balls. With that being said, the maximum amount of times that you'll screw/unscrew your shaft on the butt is 9 times in one set.
Again, this is only my opinion, but if you're playing with a decently manufactured cue there should be no wear of the joint screws even after 1000 screw/unscrew's.
There are a lot of pro's and short stops on here...and even more A level players and I'm speaking strictly from the majority, the one's that aren't in that sought after group. We don't come close to playing the number of racks that these folks play on a daily/weekly basis. I personally do have a break cue, I know that I don't need it, but that's how I was taught. I'm older now and have a better view on things. I have broke with my playing cue and I regulary break with my backup if I can't find a decent house cue.
Like I said in the beginning, this is my two cents and it may not be worth a damn to some.
Good luck and good racks regardless of what you choose to do.
Mattie