I don't have any experience with CI, but I'd understand a lot less of conversations if I couldn't lipread. I can't solely lipread and understand, i.e. watch someone across a room who I can't hear at all and understand them only by lipreading, but in noisy environments I have to look at people's faces constantly, and even then I struggle.
I liked the comment about whiplash- when I'm in a noisy pub/restaurant with a group of friends that is so true!
I don't have any experience with any kind of therapy, but I can see both points of view- it sounds beneficial in the long run to teach someone to understand more without lipreading, but then thats only if it works, for that person. I have had hearing tests where the people would stand facing away/behind me and speak, versus facing me, and the difference in my understanding is frustrating for me. I can 'hear' in that I know they have made a sound, but I have to guess as to which sound it is, from the context. The difference between hearing tests where the tester says a list of words- cat, bat, dog, frog etc and conversation is that you can guess relating to the context. It might sound, if there's background noise, like my mum is saying 'I fed the bat some new food', but as we have two cats it's more likely to be that she is saying cat.