It's better than nothing perhaps, but reminds me of UK highschool in the 80's (is it any different now?) where we had to manually copy everything down that the teacher was writing on the blackboard rather than the teacher giving handouts so you could pay attention to the teaching. The act of copying everything down was a negative rather than a positive.

Of course agentic coding tools are not trying to peer code or teach/inform you what they are doing, so being present in the moment doesn't help, but I suspect that copying it all down later doesn't help much either.

When you are/were developing software without AI, even for pretty large projects you do end up internalizing (memorizing, but not deliberately so) a lot of detail, but from my own experience I'd say it's more the design than the code. The design is what you put effort into, thought about, etc, so is both what you naturally end up memorizing, and is what you need to know to have a mental map of the project and therefore understand how best to modify it. The code itself was naturally always the last thing you did, and followed automatically from the design and module/component interfaces - not something you typically think much about other than while in the flow of just "coding it up".

By retyping LLM-generated code, it seems you are mostly going to be gaining familiarity with the wrong thing - the code and not the design. Memorizing the code is not going to help much in grokking the design.