Spaced repetition is a learning method that re-tests material at increasing intervals so it moves into long-term memory, and it's one of the most effective ways to make chess patterns automatic.
In chess, recognition speed wins games: seeing a fork, a back-rank weakness, or the right opening move instantly. Cramming a pattern once doesn't last. Spaced repetition re-surfaces each pattern just as you're about to forget it (typically at intervals like 1, 3, 7, 14, and 30 days) so each successful recall pushes it further into long-term memory.
Mainline applies this with a Leitner-style 5-box system to your weakest patterns specifically, interleaving overdue items with recent and older ones so practice stays efficient and you don't waste reps on what you already know.