Interesting point you bring up. I usually leave my carry on bag & coat in one of the storage rooms (but always keep my purse/ticket/wallet etc on my person). I've never really worried about them, but when asked by the CO check in agents 'have your items been in your possesion the whole time', I do (untruthfully) answer 'Yes'. I suppose someone could slip something into my bag during the time in the PC, or walk away with my stuff!!