To be honest I didn't even know this option existed, just goes to show how closely I read manuals (or even explore GUI's) 
 
But tonight I flipped it on, and after a lengthy recalculation had a good listen to some familiar music. 
 
The ARC2 site says "This new feature of ARC 2 improves the correction in high-end control rooms where the left and right monitors are positioned with absolute precise symmetry, improving the stereo image focus when working with elements panned dead-center in the mix - like vocals, bass, snare and so on."
 
However, my immediate impression was that it made the stereo image noticeably wider, in fact seemingly wider than my speakers when I close my eyes. Am I just imagining this? It does make my monitors sound noticeably better I have to say. 

I just tried this out on a tune with some dead center and full left/right tracks.
 
I don't know how else to describe it, and it is subtle, but with Combined L/R Correction on, everything seems more firmly placed where I have them panned.
 
I need to do more listening with a variety of material, but my initial impression is that there is a slight improvement with this on.

sharke
To be honest I didn't even know this option existed, just goes to show how closely I read manuals (or even explore GUI's) 

I recently discovered it also.  Actually made ARC useable .
http://forum.cakewalk.com/another-ARC-thread-m3525520.aspx#3528741
 

timidi

sharke
To be honest I didn't even know this option existed, just goes to show how closely I read manuals (or even explore GUI's) 

I recently discovered it also.  Actually made ARC useable .
http://forum.cakewalk.com/another-ARC-thread-m3525520.aspx#3528741
 

It was from that thread that I discovered it!

from ik's arc page:
 
Where the room is acoustically very asymmetrical, the ARC processing can also compromise the stereo imaging, most noticeably on centre-panned sounds. A combined L/R Correction mode is available to resolve such cases, where ARC 2 averages the correction applied to the L/R channels and then applies it equally to both.

batsbrew
from ik's arc page:
 
Where the room is acoustically very asymmetrical, the ARC processing can also compromise the stereo imaging, most noticeably on centre-panned sounds. A combined L/R Correction mode is available to resolve such cases, where ARC 2 averages the correction applied to the L/R channels and then applies it equally to both.

translated to layman's terms: where the mix position in the room is so bad that you probably shouldn't mix there at all, you can use the combined L/R option to trick yourself into believing that ARC can help you by smearing whatever it measured before into some meaningless average
 

well, that's not what my ears hear.
 
i think it's just some basic math calculations going on here...
 

I just realized something from this discussion.  I recently moved my monitors about 2 inches to make them a more perfect equilateral triangle with the listening position.
 
Now I've got redo the whole ARC measurement!  Damn - I should have just let things well enough alone!

Just food for thought:
 
There was a recent thread where the op noticed ARC was causing mono material to sound stereo-ized in headphones because of the phase differences between L and R.
 
Although ARC was not made for headphones, perhaps the "Combined L/R Correction" would solve this "problem" too, and/or verify that phasing was the cause? 

batsbrew
well, that's not what my ears hear.
 
i think it's just some basic math calculations going on here...
 

of course, I just took the marketing statement which is panned 100% to the positive side and panned it all the way to the ironic side ... it's up to every mix engineer to decide where to pan to their liking ...