Lately I’ve come to a greater appreciation of the importance of ‘flow’ when your SRS deck grows to a certain size–around the point where it starts to take 35 minutes to an hour to run through. I don’t allow my daily repetitions to take more than an hour, but however much time you spend on them can become taxing if the flow of your deck is poor. This problem is obviously exacerbated as the number of reps increase
Once upon a time I kept a monolithic deck, in the fashion of the day. What I was being drilled on, on a card by card basis, could switch subjects and foci within subjects with every card. And it did.
For the longest time I thought this was virtuous, imagining it had the effect of keeping you on your toes, mentally speaking, and actively involved in the processing of each card. For pragmatic reasons I eventually decided to split the kanji drills out into a separate deck, since then I could do the non-writing portions at my leisure and break out a pad of paper and a pen only when required.
It was this change that made me realize that a monolithic deck is mentally taxing for no good reason. If your subjects are all mixed together and you can be served any card at any time, every time you are presented with a card your mind has to take a second or more to orient itself regarding the subject matter. I used to think this kept one engaged and actively thinking, but now I believe it simply wastes precious energy and time. If you know you are studying vocabulary or clozing sentences or producing kanji, you don’t have to spend a moment every time a card is produced figuring out what you are doing.
What happens when your deck is monolithic, realistically speaking, is that you start to get a flow going and then you are presented with a flow-breaking card like a clozed sentence or kanji, you come to hate these experiences. However, if these more-complex cards are grouped in a separate deck with their brothers, you not only know what you are doing but can enter a flow-state with them as well.
I find separation into similar themes also, paradoxically, increases engagement with individual cards. When I am studying clozed sentences I read the whole thing and think about them, but when they are thrown in with the vocabulary I treat them as the nuisance they are and dispose of them as expediently as possible, usually only reading enough to solve.
Using the better-flow principle I’ve recently seen an uptick in my accuracy, a reduction in time spent, and a more enjoyable SRS experience in general. I still keep cards in the same deck that ask different things, so long as they don’t break the flow of their individual decks.