It's still okay to lock them but be prepared to open them in case you are selected for a random check. We were at MCO in November with our DDs, 5, 3 and 4 mos., and we just finished locking all of our luggage and checking it with a skycap who then brought the luggage into the airport and VOILA we were selected for a spot check. Of course, all of the locks were the same and we had 6 suitcases, so we had to struggle through finding the right key for each lock. The added security was worth it, though, and we were even selected for a random check of our carry-on that day too! By the way, I've vowed to color code key and lock with different shades of nail polish for future trips.