As it is just a part of general grammar, you may use it at any point in the speaking or writing.
The time when you will really be in trouble if you don't know how to use it is if you have to write about a process in Task 1 of Academic IELTS.
Think as if English is your native language. Do you always sound sophisticated, do you ever make mistakes? Or do others? Yes, you don't think of grammar or prepositions, but not because you've learned them, because you're used to it. It comes natural :) Some people are not as educated, they do make ...