To make some of the missions easier you can baricade spots with a vechile or two. EX: the Mall shootout mission you take from The Colonel/Juan Garcia Cortez. That makes you go to the Washington Mall in Ocean Beach to meet someone. Well the swat shows up. And the person you meet gets scared and runs. Well I blocked the exit he goes out two trucks. And just killed him and took what you where sent to get. If I hadn't blocked the exit he would've hoped on the bike outside. Then you'd need to chase him down. Don't get to much into blocking exits and all that with vechiles as they just might vanish. Do to the recylcing system in gta games. This makes it so the vechiles you've dumped off don't stay there and get in your way.