bb: If one answers it immediately or in a gap of less than a 2-3 days, there is a high probability for remembering the answer or the logic behind it. But the question specific memory fades away beyond that(and even if one remembers seeing the question, one may not recollect the exact answer).
But you are correct is saying that the logic will be on the memory and still can help in answering the question correctly. But I have seen myself and many other GMAT candidates doing the same question incorrect twice, specially the difficult SCs. And getting a question wrong twice makes it highly probabilistic that the particular area is very weak for the candidate(so weak that that the logic for the question itself did not stick to the long term memory) . And investing time on that area is likely to help in the overall prep.
I hope i have made my argument clear (if not strong).