You can't see out the back, and you can't haul as many people. Sometimes it's better to do a wedge or diamond shaped wall than a flat one, it just depends on many factors. Should be loud.
You pretty much dedicate the car you put the wall in, to just that.... the wall... Building an enclosure into a car usually ruins interior... Or at least makes it never the same again.. lol
Get a back-up camera so you can see behind urself, and also it takes alot of hardwork and time.
It would be a fun project... I might do something in my pathfinder once I get a new ride.
I wouldn't go through the hassle of making a wall if you aren't going to compete. and even if you are going to compete theres a ton of mods you need to do before you put a wall in it.