Jockstraps help with BDP (Big Dick Problems). I have a rather small frame with an above average sized cock, wearing a jock helps "dampen" clothing bulges and also prevents your junk from passing between your thighs. During workouts it prevents cock flopping, noticeable hangs, and keeps everything out of the way if you will so you can focus more on what you're doing. All of the above is the case with your normal athletic jock. Designer jocks on the other hand do the exact opposite. They put everything "front and center", "lift and accentuate", and of-course "provide easy access".
Designer jock brands: Cellblock13, Papi, and Diesel to name a few.
Athletic brands: Bike, Safeguard, Duke, and Stafford to name a few.