Juan Melara has written a bit about the Color Space Transformation tools in Resolve on his blog:
http://juanmelara.com.au/blog/
I think a lot depends specifically on what you're trying to do and the nature of the ProRes material. I generally don't use CST and find a way to do it that's faster and simpler, but there are advantages to that method. It's mandatory if you're (say) dealing with EXR linear footage.