Yes, you hold on to it until you get an RFE asking for it, or bring it to the interview. But the RFE process may delay your I-485, so it is usually best to file the I-693 with the I-485. But if you are trying to get the I-485 filed this month before the fee increase, and there is not enough time to do the medical before then, then not filing I-693 with I-485 is reasonable.
Biometrics is a separate thing. They will tell you where and when to go.