There are so many reasons to check a flop that hits you. One reason to check a flop is to keep the pot low. Lets say u have Q6s in the sb and the flop comes Q 5 2. You don't want to generate a big pot with such a weak kicker.
Another reason is to trap. Lets say u have K10 in the bb and the flop comes K 8 4. You know that more than likely you have the best hand and all you have to worry about is an ace beating you. The odds
of an A coming on the turn is really low so its best to check and hope the turn helps your opponent. Ofcourse if you are going up against 2 or more opponents it is wise to bet the flop and see where you are in the hand.
Another reason pro's like to check the flop is to show their opponents that they don't always bet out when they hit a flop. Your opponents might think twice about bluffing them next time, if they think they might be trapping.