from what I hear turndowns at the muffler with no tail pipes can cause an annoying resonance inside the car as well as blowing dust up at stop lights. The only benefits I see are hiding the exhaust and not having to add tailpipes........esp tough with aftermarket rear suspensions.
No Offence to anyone but....My biggest memory of turndowns are of a 1968 Camaro I was watching going thru the Turkey Runs at Daytona Speedway. I watched how the exhaust sandblasted the car going thru the paved road with dirt on the surface. Then he turned down a full dirt access road and the car was engulfed with dirt............that was enough for me.....I guess it depends on where you go..........I did like sound though with a radical cam