I've flown both Intra and Inter China and never locked my bags. Nor has anyone mentioned to me that I should. But it does bring up an interesting situation if one is flying Inter-China from/to the US. Since TSA frowns upon locked baggage (unless of course it is locked with their own "special" locks.) So one country wants you to the other doesn't. Sounds like fun to me.

Given that I carry on most anything of value with I fly, I have never had any instances of anything growing legs and walking away.