Several people have mentioned this overkill theory, and I'm not sure I buy it. What application is there that requires the energy of the .338, but the .50 is way to much.
I can't speak for others, but my reference to "overkill" is related strictly to cost...
If a different weapon platform and caliber can achieve the same objective for far less cost- not to mention the size and weight of the platform as relates to mobility- than that would be "overkill".
My point wasn't related to energy, in a target application it would be irrelevant.
Far cheaper to get your hands on- and shoot- a .338 LM capable of sub-minute accuracy than a .50.