Tweaking the parameters may just be a 1% improvement in terms of learning and retention. Perhaps even no improvement at all.
Where the improvement is seen is in the use of your time.
The problem is that people incorrectly assume that they must "do something" about missed reviews. That's just not how it works; in fact, Anki will give you extra credit for recalling a card beyond the expected forgetting time, so working with a backlog of cards to review is a lot easier than it sounds.
The whole idea is that once the expected forgetting time for those "review" cards has been pushed far in the future, that's the best time to learn new, more challenging content. It works very well in my experience.
Where reducing the amount of reviews may well be justified is for cards that are "nice to have", but that you don't actually care about remembering. That's also the only sorts of cards for which "leech" protection makes sense, and that's a lot closer to a poor default in my view.
> I know many people who try Anki out, and then go down a rabbit hole learning as many features as possible so they can use it “efficiently”. Usually, they're chasing 1% improvements. Often, those people ultimately give up Anki as “too difficult”, which is often a synonym for “I got nervous I wasn't using it perfectly”. This is a pity. As discussed earlier, Anki offers something like a 20-fold improvement over (say) ordinary flashcards. And so they're giving up a 2,000% improvement because they were worried they were missing a few final 5%, 1% and (in many cases) 0.1% improvements. This kind of rabbit hole seems to be especially attractive to programmers.
[0] http://augmentingcognition.com/ltm.html