[asdasf]

Because they are a solution in search of a problem. Or more accurately, they are a problem in search of a problem.

http://wiki.postgresql.org/wiki/OptimizerHintsDiscussion

[Farox]

Hmm, I needed them a few times so far, specially when it comes to lots and complex sets of data and complex queries.

I had jobs run for a few hours on Dev only to take weeks (if I would have let them) on production, which was in ever aspect a beefier machine.

[asdasf]

99% of the hinting I've seen people "need" was not needed at all, it was just the lazy way to temporarily work around a bad query plan. Other than actual bugs in the query planner, I can't even invent a hypothetical scenario where the tools postgresql already gives you to influence the query planner couldn't solve a problem.