If you answer questions in a way that's not inline with what you actually want, then someone may answer inline with what you said you wanted, rather than what you actually wanted, and that will artificially increase their match score. Also, if you take a very important question and weigh it lower, then someone answering that question correctly won't boost their match score as much as it should. Or, more commonly, if you weigh a question too heavily (especially one where most answer in the expected way), then it will greatly exaggerate someone's match %. Answering irrelevant questions will dilute the distribution of the match %, and give people an increased score for answering questions you don't care about. For example, if you answered 10 questions, but 8 of them were irrelevant to you, then someone could correctly answer those 8 questions only (skipping the other 2) and even though the other 2 are very important, they'll still get an "8/10." This will make it seem as though they are great matches, even though they really aren't (would answer the 2 questions you care about incorrectly).