I had a 2012 F150 3.5 Ecoboost, that was at 140,000 miles when I traded it for my new truck. I never had an oil catch can on it, and never had any issues. So I wouldn't say it is a NEED, but it may help to prevent future issues, or the need to clean the intake valves.
The new 3.5 Ecoboost has both direct injection and port injection, so there is now a fuel injector spraying fuel at the back of the intake valve, and will prevent any oily build up.
There was a pretty good discussion on the Tremor forums about it. Do you need it? Most say no, some say its a good idea. Does it hurt anything to have one? As long as you remember to empty it, it only hurts the wallet with initial purchase, and the time it takes to install. If it's worth it to help you sleep at night, go for it.