"Well, no one uses LCSH anymore do they? I mean, it's all just keyword searching now."
Nooooooo. All those hours trying to get those semantic relationships just right...please tell me that someone cares!
After all, Great Britain -> Foreign Relations -> United States
is the total opposite in meaning to
United States -> Foreign Relations -> Great Britain
and if the book was about both, then LCSH give you a way to exhibit both.
Not quite the same as just typing 'Obama' and crossing your fingers now is it.