I would argue that for the vast majority of the people carrying weapons, the only reason not to have a round in the chamber is to avoid an accidental (or negligent) discharge.
Almost all newer guns, and certainly all newer guns with decockers, have firing pin blocks. If equipped with a firing pin block, the gun can't fire if dropped or if the hammer is forcefully struck; it can only fire when the trigger is pulled (generally, all the way to the rear.) Most striker-fired guns have similar safety mechanisms.
Carrying any gun equipped with a firing pin block with the chamber empty assumes that the person carrying, if he needs to use the weapon, will 1) have the time needed to chamber a round, and 2) will have both hands free to do it. I don't think that is a safe assumption.