But I did find that I need to turn it off at certain stages when learning (or re-learning) a programming language. It's seemed counterproductive until you have a good grasp on the basic syntax of the language. But the "showing you new APIs" does seem to be a thing that actually helps.

In general, you should not be accepting code completions that you don't understand. I'm usually stricter, in that I only typically accept completions that line up with what I was planning to type anyway.