When you have the laser guided missile it can only tell if you are aiming at a hostile vehicle, but not if it is occupied.

This can come in handy when you have a target, you just can't shoot, but if they have a enemy origin vehicle near them then lock on to the vehicle (note: the car does not have to have someone in it) and then when you get to guide the missile just plant that bomb were the enemy is.

You dont have to hit the car and then BOOM!

Then sit back and watch the fire works.