Chuck Ahrens is relatively unknown to most modern lifters, but in his time he was considered to have the strongest shoulders and arms in the world. He was so wide he looked unreal.
In his prime, Ahrens could do reps with 200 pound dumbbells in the shoulder press (some people even claim to have seen him press a 300 pound dumbbell with one arm), and do 28 reps with 405 in the bench press.
One of his shoulder exercises was very peculiar: he'd do overhead dumbbell presses, but instead of pressing them straight up he'd press them up and away laterally, basically doing a "V" with both arms. He had no choice but to press in this manner because he used special loadable dumbbells that were very long. Pressing them straight up was impossible without the 'bells hitting each other.
What this exercise does is place the shoulders, especially the medial portion of the deltoid, under greater tension as the movement gets completed.