Just extra "visual noise" on the rear end maybe? I'm sure some ppl will do it so they can say their 128i is a 135i to casual bystanders, or maybe a 135i owner wants a "sleeper." Seems to be done on more and more cars these days... I see debadged BMW's, Acuras, Hondas, Audis all over the place.
Then there's the opposite trend of adding badges that make no sense... maybe I'll put a "Type R" badge on my 135i.
2014 Tesla Model S 85kwh
2011 335d / Deep Sea Blue / Saddle brown / sport / premium
2008 BMW 135i / 6MT
2002 Z06 Corvette