oh, the never ending question.
With respect, if your not touring with a million dollar carbon fibre frame, why not consider letting your carrier decide. My airlines say I should use a cardboard box or plastic bag (bars turned, pedals removed and tyres deflated).
I use a plastic bag. I buy 2 and bike to the airport, legalize the bike by doing the above, and stick it in one bag. The other bag I keep for the return trip. They are nicely folded and only weigh less than half a kilo. They tuck in the pannier really easily.
Until I did that I had to return from the same airport, hire someone to look after my box, and drag it through the airport. It's not worth the trouble!
By the way, I have received some damage from using a plastic bag. Until I started to bungee the front wheel the the frame, I'd get wheel damage. After that I've got rub damage in the form of scratches and knicks in various places. I've always been able to bike away from the airport though.
If you've got a touring beauty that you don't want a scratch on, then it will cost you in convenience and big time in money and time.
My advice is not to tour with a show bike. A few battle scars make the bike more interesting.
Now, you will hear from the other crowd.