When is it good to bring in outside knowledge: when it helps you construct a logical argument. For instance, if you knew that non-commercial planes weren't required to have transponders (and I have no idea if that's true - I'm not a pilot
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) that would help you notice a big flaw in that particular argument. It only talks about putting transponders in commercial planes, and claims that this would nearly eliminate collisions - but are commercial planes really responsible for all collisions? Or if you had observed a failure of a transponder before, you might immediately think to question the argument based on whether or not we can really be certain the transponders will work.
When is it bad to bring in outside knowledge: when it leads you to make assumptions of your own or take things for granted. For instance, if you knew that non-commercial planes
were required to have transponders, you might very well miss the potential counterargument that goes "how do we know that ending collisions among
commercial planes would nearly eliminate all midair collisions? What about, for instance, private planes?" After all, even though the argument only talks about commercial planes, you, personally, know that it applies to noncommercial planes as well. The problem is, since the argument doesn't
say that, it's still a flaw in the argument. Some of my students have had success pretending that GMAT prompts and arguments aren't actually describing the real world. Instead, they're describing an alternate reality, and the only things you know about that reality, are the things the test tells you.