There is a differance and a need for a catch can depending on what you have. If you are supercharged it is recommended. If you are not than I would say it is optional. The stock setup does have mesh material underneath of the valve covers that is there to trap oil and keep it from being routed through the PCV hoses and reintroduced into the intake path. A catch can such as Justin's can be added as another means of trapping the oil but usually it is only a real problem when supercharged.
I once had a bet with friends on who among us could get married quickest. I took first, third and fourth place.
05 Fire Red QC SRT-10. Roe supercharger, 180 thermostat, Demon coils, carbon fiber graphics, Magnaflow cat back; SCT & Roe Racing tune; hard pipes; billet fuel rails; Bellanger headers; catless mids; LED taillights, JTSVP venom hood, custom side exhaust, minitubs, dual fuel pumps.
2006 Ram SRT-10 RC. Roe supercharger, 170 thermostat, QA1 shocks, Belanger headers, Aluminum driveshaft, Forged engine
2006 Saleen Supercharged Mustang
2004 Saleen Mustang Extreme
1999 Ford Mustang Cobra convertible
2006 Dodge Charger R/T "Monster SEMA car"
2007 Jeep SRT8
2002 Big Dog Pitbull
2005 Saleen Supercharged Mustang
2011 Ram Express. Stacey David/Gearz TV Drag-N-Wagon build.
2006 Saleen Mustang Extreme