Adam, It's also posted in the 2 rail category.
So your posted question may have different answers depending on who's reading it.
@Adam ND posted:
I’m obviously missing something, what is the reasoning for using the Kadee couplers in the first place. Just trying to understand. Thanks in advance.
To add to the answers above:
If you're a 2 rail person, there are better scale choices. The KDs work great and attempt to get a scale look.
If you're a 3 rail person, changing out all your couplers may seem crazy. I would suggest looking around at what different posters are doing with each RR they build. Some just plop trains on the track and have their fun. Some are after a better looking RR that captures more realism.
Both are great and both are correct!
Edit: you may also wish to look up the definition of the 3RS movement. That may help you understand what is happening in O.