One of the cool things in ARMA is the ability to command your squad.
Eg. having all your units hold fire, then wait for an enemy squad to come by, then telling everyone to "Fire at will".
In ARMA 1, when piloting a helicopter with a gunner, you could lock onto a target and say "Fire", and the gunner would fire a missile. In ARMA 2, this was changed to have the gunner fire the moment you started saying "Fire" rather than after, which really killed the immersion back then.
Now in ARMA 3, this applies to all commands given to AIs. They receive the order the moment you start issuing your command, rather than after you're done saying it.
This really kills it. It's like you're now dictating what your units are doing rather than telling them what to do.
Note, that this does not seem to apply if you're commanding "ALL" at the same time. But if you select all your units but one (or less), they'll do whatever you tell them before they hear you say it.