I'd have to review the slide to be sure (i.e. is there a specific problem that these comments referred to?), but it sounds like these generalizations assume that the easy statement is insufficient.
In practice, clear insufficiency is often the reason a statement is considered "the easy one." Flip through the OG, and you will find statements that mention 1 variable when clearly 2 are needed to solve. You'll even find problems that ask about some variable(s), and a statement that ignores those and instead mentions completely new variable(s)!
So, all easy statements are not insufficient.
But, if the statement(s) are easy
because they are insufficient, start there and cross AD/BD or ABD, as the case may be.
tgb3 wrote:
In addition, according to the instructor’s comment: “You need to implement this strategy ONLY IF there is no or very little info in a question” – Why is that?
I would not say you "need" to implement this strategy when the question stem contains minimal info, but rather that you should NOT implement this strategy if there is SOME info in the question stem.
The info in the question stem might combine with the info in an apparently insufficient statement, in a way that is not immediately obvious, to allow you to answer the question. To eliminate A,B, or D too fast would be dangerous in such a case.