So now that you've learned how to animate a walk cycle using rotoscoping, let's talk about how much you'll need to do it.
Admittedly, the process can get a bit tedious, especially if you're doing 10 frames. With a standard 4 direction view, we're talking 30 frames of animation per walking character (assuming you're just flipping your side view.) The question then becomes: how many of your characters actually need full walk cycles?
It all depends on your game. You might have a huge cast of characters, but none of them might ever have to move from the spot they're in. Or, you might have several characters that follow the player, or just walk around to add a bit of atmosphere to things.
Let's take a look at some well-known adventure games. In Sierra's King's Quest VI, nearly every single character has a full four direction walk cycle. Some even have diagonal views! Most of them are 6 frames, but it's still a lot of work, especially considering the majority of them aren't ever actually seen in-game. In fact, it was like this for most Sierra games. LucasArts games, especially the ones made in the early to mid '90s were the same.
Two notable exceptions are Full Throttle and The Curse of Monkey Island. In these games, only the main character has a full walk cycle. Secondary characters who are shown walking only do so for a few frames, animated as needed. It's especially understandable in Curse where you had traditionally hand-animated cutscenes as well as sprites, but I wonder how much of it was due to budget constraints vs creative decision.
Then you have games like Broken Sword, which were also animated with traditional cel animation, but several characters have walk cycles. So does this mean games with more walk cycles are better? Not necessarily, but it will surely break immersion if you are in a crowded city street and everyone is just standing around not moving. Worse still, if there's nobody around at all.