Read the rules carefully, and you might be confused.
In melee combat, you can help a friend attack or defend by distracting or interfering with an opponent. If you're in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can attempt to aid your friend as a standard action. You make an attack roll against AC 10. If you succeed, your friend gains either a +2 bonus on his next attack roll against that opponent or a +2 bonus to AC against that opponent's next attack (your choice), as long as that attack comes before the beginning of your next turn. Multiple characters can aid the same friend, and similar bonuses stack.
It turns out, according to the rules the best way of protecting someone isn't by being next to them. It's by being next to the person attacking them.
I could almost buy that, except that the following feats use Aid Another as a core mechanic-
So now we have a problem.
A guy with a shield is a bad bodyguard. What you want is a guy with a polearm! You don't want your bodyguard next to you. You want them in the middle of as many enemies as possible! Their ability to protect you is contingent on how many people they Threaten with their weapon, not on weather they are between you and someone trying to stab you! Someone should probably tell the Secret Service they're doing it all wrong.
Bodyguards are also completely helpless against ranged weapons. There is no such thing as "taking a bullet" for someone. It can't happen. It doesn't even matter if the bodyguard is threatening the shooter. All they can do is take a normal AoO and hope that shot they couldn't stop wasn't an Arrow of Slaying.
Basically, Bodyguard and In Harms Way are counter-intuitive and bad.