[Elecraft] K3 Speaker Amp Protection

[F. Barry McWilliams]

Don, Joe --

Don, 
You missed my point. of confusion,  Joe said "open circuit". 

Yep, I do use a stereo plug, thus I have an right channel "open circuit" when I connect an external
speaker.  

But there seems to be something else that Joe is warning against  other than
"open circuit".  Referring to Rev C, he says,
"This is an entirely different (and older) modification.  Output Mod
Rev C is designed to prevent damage to the right channel of the AF
amp when it is "open circuit" as it is when SPEAKERS=2 with a single
speaker attached."
So what is the problem with an "open circuit" right channel speaker?
TNX again