To make some missions easier. For the ones that have spots you can block off with one or two vechiles. EX: for the mission Friggin The Riggin you do for Donald Love. You take in Staunton Island. You need to destroy the inside of a warehouse and more. Ain't say the rest, cause it would give away the rest of the mission. I drove a patriot inside the warehouse and ran over the enemies that I could and just shot the rest. After I did that I used the patriot to block the entrance to the warehouse. Making it so the waves enemies that came during your destruction of the warehouse couldn't come in. Don't put to much work into your baricade, cause it might just vanish. Do the recycling system that gta games have. So you don't have all the past vechiles you dumped off in your way.