I have the polished JLT on driver's side of my 2010. With oem Ford motorcraft semi synthetic 5W-20 eng oil, the JLT would catch a helluva lot of oil, like 80% full after 6 months. Then switched to RP 5W-30 HPS, 100% synthetic.... at which point, the JLT has very little in it, maybe 10% at most.
With the oem ford semi synthetic 5W-20, the catch can was not only 80% full, it looked like a chocolate milk shake. Mixture of oil, unburnt gas, and moisture. With the 100% synthetic, no more choc shake, it looks like plane jane new eng oil..and very little collected. Several of us noticed the same effect after switching to 100% synthetic. I have no explanation for that effect.
Without the catch can, you end up with a mess inside the blower elbow on a PD blower, and also oil all over the IC, and also all over the aluminum manifold. It also lowers the octane rating of what ever gas you are using at least one point. Installing 2 of em, nose to tail, in series, like skwerl does, is a good idea, esp if the 2nd one is catching whatever the 1st one misses. Easy enough to do.