I received my BMS catch can and installed it yesterday. At $179 you guys that are running performance mods it's a great bolt on kit that takes about 25 minutes to install. The construction of the can is excellent.
WHY USE A CATCH CAN:
A catch can is used to aid in the reduction/elimination of Blow-by. Blow-by is caused when a combustion in the engine forces fuel, air, and moisture past the piston rings and into the crankcase. From there, the blow-by is released by the crank case vents and back into the intake pipe. This occurs on all engines, but is worse on turbo engines due to the stronger combustion. If you don't have a catch can that excess crap will build up in the valvetrain, turbo, intercooler, and intercooler piping.