I think it’s totally fine to have basically one deck for everything. I have such a deck, containing history facts alongside math alongside friends’ birthdays, and this is not a problem.
I think this was fine with the old anki algorithm, but less so with FSRS. It’s sensible a priori to expect that your forgetting curves for birthdays and math are different. If you optimize parameters for a single deck, anki will treat every card in the set {birthdays, math, historical trivia} the same. But if you have separate decks (and deck groups) for each topic, FSRS will be able to extract more signal and pick better parameters. Admittedly, using a single deck probably isn’t a huge mistake, but it seems like an unforced error to me.
I think this was fine with the old anki algorithm, but less so with FSRS.
It’s sensible a priori to expect that your forgetting curves for birthdays and math are different. If you optimize parameters for a single deck, anki will treat every card in the set {birthdays, math, historical trivia} the same. But if you have separate decks (and deck groups) for each topic, FSRS will be able to extract more signal and pick better parameters.
Admittedly, using a single deck probably isn’t a huge mistake, but it seems like an unforced error to me.
you can use subdecks and get best of both worlds
both good points, thank you!