Hey Achieve,
I love this question so hopefully Jim doesn't mind if I chime in here.
The way that the GMAT scoring algorithm is set up, it's a lot like a game of "Twenty Questions", in which your responses to questions help the test answer questions like "are you above a 600?" (YES), "are you above a 700?" (NO), "Are you above a 650?" (YES), etc.
The tough thing about answering 7 in a row wrong is that the computer starts to doubt its previous data about how high your score was before. When you get a question wrong, it feeds you a lower question to help figure out "the bottom" of your score range, and when you get one right it feeds you a higher question to see what your peak is. And, of course, since you can guess correctly or make a silly mistake on something you should get right, the test has to account for "false positives" and to a lesser extent "false negatives" (I say a lesser extent since you could make an argument that silly mistakes should still count against you, whereas blindly-correct guesses provide b-schools with bad information...that has to be dealt with!).
So if you know that you're going to need to guess a few times here or there, it's not a bad idea to spread them out and give yourself a guess every 9-10 questions* or so. If after 20-30 seconds you're staring at a question and thinking "there's just no way...", guessing banks you 90-100 seconds that you can use on a later question, and there's a decent chance that if that's the case you're guessing toward the peak of your ability, anyway, so there's a fair chance you would have gotten it wrong and that the next question will be back in your wheelhouse so that you can continue "climbing" again.
(*that's about the most I'd "intentionally" guess...3-4 for the section. Obviously if you don't need that many guesses, don't burn them, but if you're routinely having to guess on 5-7 questions, strategically you probably need to assume that and plan ahead)
And the main benefit to that is that, if you assume that you're going to guess on some questions and that you're going to get some wrong, you spread them out so that you don't hit that point where the test starts to doubt your ability level because you're just spiraling downhill.
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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