I have read this thread again.

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2757170

It made much more sense after reading everyone's replies in this thread. Thank you.

No wonder I was confused!

So failure to GC does not, in itself, cause images to have blown out highlights and yellow blooms. Rather it causes the images to be darker. At least, that is what I get from that thread:  it certainly is the case in my renders.

But since I always postwork, and GC is much simpler in photoshop, I guess the exhortation to GC is for people who don't do any postwork...

And yes fiddling with hundreds of material nodes is not my idea of fun. I'd much rather render in 12 passes and composite with 10 different background sources, while creating a series of 900mb PSD's with 70 layers in each. I'm guessing the node gurus feel exactly the opposite. :)