I ride an S&S coupled Waterford Adventurecycle. I have done about a dozen tours on it since 2004. I've taken it apart and put it in a standard sized case and flown with it many times.
I've never ridden a non-coupled touring bike but I can't tell that there is anything unusual about the bike I tour on.
The only difference I can see is that you have to carry a separate spanner/wrench-like tool to deal with the couplers.
The main reason for the couplers is to allow you to travel with the bike easily. While I do fly with it, it also makes taking the bike in a car very easy.
The highest recommendation I can give it is that if I every have to buy another touring bike, I will certainly spend the extra money to get the couplers installed on it. I had mine installed when the bike was built. I have no experience with retro-fitting.
Here are some photos of how I get the bike into the box
(it always seems to take about 2 hours.