Adults understand rules, while babies don’t. Thus, sometimes it can be useful to refer to rules.
However, usually study time is so skewed towards grammar that I’d rather focus on speaking in my lessons.
In any case, speaking works for everyone.
You have a point in that, as long as people are not challenged to speak, they might feel safer because they “understand” rules, but when it’s time to speak… they go blank.
Besides that, the older, the more likely it is that they were exposed to and are used to obsolete methods.