I'd say one of the main benefits with Anki or SuperMemo is that the automation of the algorithm allows for many more variables than you could track manually. For each card, the history of its reviews can be remembered and taken into account―e.g. both Anki and SM have several possible answers for how well you remember the card instead of just "yes/no," varying the next interval relative to the previous one. You can tune parameters for each set of cards, allocating more or less attention to them depending on how easily you remember different kinds of information. This control, IMO, optimizes the schedule over the course of months. (Though it does make tweaking the params rather complicated sometimes.)