Avoda Zara 19a - Learning To Remember

The gemara discusses learning styles such as learning superficially the entire Torah even at the expense of remembering and even at the expense of depth, and only afterward learning in-depth. Furthermore, the gemara points out that one should be a רמאי in the sense that he plans out his learning to enable the best retention and supports this with a parable of a bird trapper who breaks the wings after each capture (although it takes time to break the wings and he catches fewer birds, at least he will retain those that he captured).

The Shulchan Aruch of the Ba'al Ha'tanya (kunteros talmud torah chapter 2: 5-11) has an elaborate discussion about the prohibition to forget one's learning and when it applies. He explains that if one knows himself to forget very easily, their learning must be organized in a way that allows for the most review even at the expense of covering ground so that he doesn't forget what he has learned. He explains that we find even the chachamim of the talmud were sometimes experts in only one or two tractates, presumably because they were preoccupied with reviewing that they have learned and were unable to move on. A person like this must prioritize the areas that are practical so that if he leaves sections of Torah untouched, it will be the areas that are less practical. Most of his approach to limud ha'torah is very practical and rationale. The only exception is when he describes the type of individual who spends almost all his learning time on review so that he doesn't forget. This individual, if left with some extra time should use it to study the areas of Torah that he otherwise wouldn't get to, even if he will cover them only once and most likely completely forget what he has learned. Why?

כדי שיוכל ללמוד כל התורה שבעל פה כולה פעם אחד בחייו לקיים מצות "שמור תשמרון את כל המצוה" וכו' ואף שישכח הכל, הרי לעתיד לבוא יזכירוהו כל לימודו ששכח מחמת אנסו שאי אפשר לו לחזור כ"כ שלא ישכח לימוד זה שלומד רק שעה קטנה בכל יום, כי שאר היום והלילה צריך לו לחזור על לימוד המביא לידי מעשה וכו

Here he deviates from the practical and enters a more chassidic realm where he says that the entire Torah should be covered at least once in a persons lifetime, even if there will be no retention (but of course the large majority of his time and energy should be invested in reviewing the areas that he will remember).