I've watched the tutorial video a few times now at the section on Create other Keyframes (about 13 mins in on the HG tutorial) and I can't figure out this stage of the process:

Why create other keyframes in the first place-I can see Gunther does it for good effect with colour toning BUT How do you know whether to do this or not from looking at the curves etc in LRT?

How many do you need - you can have from a couple to 20 - and where do you place them-is LRT estimating this for you?

I have just started doing these, but I think its because you may want to have the color changing at spots other than where the keyframes are. Or in my most recent case, I had 9-1 stop jumps during a 600 image, Holy Grail sunset. I didn't really want to fix the color 11 times, so I just did beginning, end and 4 equally spread out in the middle which still gave me nice color transitions throughout the video

Exactly thats the reason. Normally for color adjusting you will need a lot less keyframes and rather even spaced and separated from the holy grail "jumps".