Actually this feature wouldnt be entirely useless.
Say there could be one mission where you have to drive through a rival gang's territory, to draw the the attention to you (so someone in your gang or that you are working for, could, lets say, blow up the enemies HQ). Since you are gonna be drawing all the gunfire, you go to your local chop shop and armor up a hermes or something, maybe add a bigger engine, so you can plow through the gang members easier. That way you can drive through the gang territory, without the risk of your car blowing up.
Besides, who wouldn't want to see a manana with inferus like abilities?