In the end, doing partial reps means you can use more weight. Some exercises - when focusing on a particular part of the ROM - have been all-but proven successful in developing the specific part of the muscle that the ROM focuses on. If you focus on the lower half of bench press, you'll develop a wide chest, but likely have fairly flat inner pecs. If you focus on the top half of the biceps curl, you'll likely get peaked biceps but lose fullness down the arm to the elbow. How it relates to shoulder presses, I have no clue.