For me, I 1st got reps to test them out and see how they felt, and how I felt wearing them, before buying the real thing. The 2nd reason was to have the same watch to wear while doing things where I could possibly damage the watch, or if I am in places that there is a possibility of getting jacked, like while travelling, etc... if i'm wearing a rep, go ahead, take it!
I also feel that counterfeiting is really an artform.
I love my real watches because I like to swim with them, but I get more compliments on my reps than my gens, and I get accused of my gens being reps all the time. I just installed a saphire caseback for my Sub (from Thomas Preik) and nobody believes that it's real anymore