Although I do not use it myself, I had seen that some other people do, and that apparently you cannot disable autocorrect while still having prediction enabled (at least, that is what they told me); I think it might be useful to enable prediction without autocorrect.
What are you talking about? Auto-Correction and Predictive Text are 2 separate toggles in the keyboard settings.
I have Auto-Correction enabled, and Predictive Text disabled. I can switch it around the other way too.