Hey, thanks for posting the link Weiss, I wasn't aware of Greg's 'after hours' vids. and I like what I've watched so far.
As a dude, I can already vouch for Greg - he did a bang up job with a plug-in of a hardware unit I put together for Hugo Nicolson and I still receive a small stipend royalty from Kush c/o Hugo.
I think the LCR video made a lot of sense personally and it's something I stumbled on myself (alternately muting each side) when I was more involved in that stuff.
As for the mono mixing video, I also get what he's saying there. It isn't about setting level balances which, more often than not, I found needed a bit of a rebalance after spreading into a stereo image. But what I got is that he was looking at conflicting or overlapped frequency ranges of parts and carving out with eq etc to seperate them. I can see how this would be useful. It would also be useful when coming up with parts as it could more easily show where it might be beneficial to use a different inversion or voicing etc.
Within reason, I don't see any point in worrying about absolute mono compatibility these days. Sure, a lot of stuff might get played on an iPhone without headphones by some but, are we really wanting to conform downwards to the lowest common denominator?