As a general rule, don't play rags, suited or not. Stick to good starting hands. Just because you see a flop of 6-6-5 after mucking a hand of 5-6, doesn't mean you made a bad call. This is going to happen from time to time when you lay a hand down, if you were to use this logic, no hand would be poor enough to throw away because there is always a possibility to have the "nuts" after the flop with even the worst of hole cards.
Having said that, if you are typically a very tight player and have a good solid read on your opponent, limping with suited connectors is sometimes a good play to change your game up a bit. However, I usually try to stay above 8's when I make this play, sometimes going down as low as 6-7, but very rarely. The idea here is to try and improve your hand and take down a pot by either it improving or bluffing
at it. You want to do this to keep the other guy guessing. If he thinks you may limp or small bet cards like this he's going to give you more action when he has a decent starting hand in the hopes that you're again playing rags. After making a play like this and either winning a pot with rags or being busted trying to take a pot with them, tighten up for a little while afterwards and wait for premium hands. Your opponent may lower his expectations and play a smaller starting hand because of your previous play and you can take his checks with your premium hand.