Punch Button on Console

In the V-Studio 700 manual, there is a section about punch in.  It says to push the Punch button, arm the track, and then use the record and stop buttons to start and stop recording.
 
So, what is the purpose of the punch button?  If a track is armed, hitting record will punch in whether you press a punch button first or not.  If you are doing auto-punch based on time markers, you shouldn't have to hit record at all.
 
The only thing that comes to mind is (maybe) if you have Preferences set to sound-on-sound, the punch button gives you a temporary replace/overwrite instead of sound-on-sound.  Is that it?  If not, I don't know what the punch button does and the manual does not seem very clear.
 
By the way, I cannot image why sound-on-sound is the default in a DAW with unlimited tracks.  I have to go in and reset all that stuff about s-o-s v overwire, new layers, etc. on every project.