It doesn’t help retain the information, it brings the information back out. The problem is, most humans only maintain a part of a memory, not the whole event. There are memories where you can remember everything, but most of your memories are from events that you took an exceptional note to. Example: You have a birthday party, of course friends are invited. They all bring gifts. Some bring great gifts and some bring cheap ones. Depending on the type of person you are, when you remember your birthday party, you might only remember the good gifts (or vise versa). Its the same with studying, when you actually take the test, you look at a question. Then all of a sudden, you get excited because for some strange reason you instantly remember the answer to it. Your mind catches something in the question that links it to something you studied a day ago and makes an instant connection, bringing up a memory from when you were studying. Sorry for getting technical. Here’s an easy way to see it, A computer has tons of information, but you can’t see it. But when you go to the search bar and type “r”, the computer brings up every piece of information with “r” in it. Then it’s up to you to choose what your looking for from those results. That’s how our memory works.