I think this is entirely depending on the attitude or mindset you have when approaching the teaching task, at least for technical subjects.
If you're trying things in a vacuum, do not get reviews from people in know of how things work, do not do research past "this seems to work for me, time to disseminate", you will probably be missing on a lot of content.
People who get to the task by actually forcing themselves to learn first, get some peer reviews, go straight to sources and take a broader mindset of "I have to get this right because it costs more time and energy to undo bad teaching than teaching in the first place" might do better. In fact, they might get the benefit of teaching while still having a fresh perspective on a given topic, something extremely lacking with some teaching material.
If you're trying things in a vacuum, do not get reviews from people in know of how things work, do not do research past "this seems to work for me, time to disseminate", you will probably be missing on a lot of content.
People who get to the task by actually forcing themselves to learn first, get some peer reviews, go straight to sources and take a broader mindset of "I have to get this right because it costs more time and energy to undo bad teaching than teaching in the first place" might do better. In fact, they might get the benefit of teaching while still having a fresh perspective on a given topic, something extremely lacking with some teaching material.