Flashcards should be taking up about 10% to 20% of your language-learning time. To see how I've arrived at that range, let's start by considering the two extremities of the flashcard use continuum.
Point A is no flashcard use at all. This is Randy's stance. Point B or thereabouts, on the other hand, represents the other extreme: you're using flashcards as your main way to learn a language. When I read Randy's criticisms of flashcards, it comes off to me as if he's throwing those criticisms at someone who's at or approaching point B as their language-learning method, i.e., pretty much the only thing they're doing is using flashcards.
I think Randy's completely correct in that, as a language learner, you don't want your language-learning time to be anywhere near point B. If you simply try to remember a string of facts without every actually applying them, Randy's completely right: you're going to struggle to ever get your speaking off the ground.
Where Randy and I disagree is how much you should draw back from point B. He takes the extreme position that flashcards are verboten and you shouldn't use them at all. I think the ratio should look something more like point C:
So my position is that you should be spending roughly 10% to 20% of your language-learning time using flashcards, although you might want to bump that up if you've been going through particularly vocab-rich content. (And, as noted previously, the ideal situation is where all of that time is trapped time.)
Let's illustrate this with a couple examples. Let's say you're spending one hour a day studying your target language, and you don't want to take away from that time to do flashcards. You'd need to add 7 to 15 minutes of flashcard usage every day to hit the 10% to 20% ratios, and I'd wager that pretty much everyone can easily come up with that much trapped time every day. To take an example at the other end of the spectrum, let's say you're spending 8 hours a day learning your target language and, again, you don't want to take away from those 8 hours. In that case, you'd need to find an additional 54 to 120 minutes to reach those ratios. An hour of trapped time seems fairly common (I tend to get something over 60 minutes of it per day), but I doubt 120 minutes is. However, the higher the number of hours of exposure goes the more likely the 10% ratio is going to be closer to the mark.
So what's the rest of the time used for? Getting the exact same in-context exposure to the language that Randy recommends, i.e., reading, listening, writing, and speaking.
In other words, at the end of the day, flashcards should only supplement in-context exposure; they do not replace it.
Remember this little chart? Here's a slightly updated version:
You see SRS sitting way up there in the top right corner? It's just one of the many kinds of exposures you could be getting, and that's the way it should be.
This post is part of a series on using flashcards written in response to Why I don't use flashcards (and you shouldn't either) and other related posts on Yearlyglot.com.