(I'm by no means in the situation described below, I'm just hypothesizing/daydreaming.)
Say that a professional mathematician thinks that he can get some interesting results by applying a certain method he found. Being a seasoned mathematician, he is confident in his attempt, only to find out that the results yielded by the method were trivial. Is it still meaningful to publish the result, as to tell other mathematicians that come up with the same method "Hey, I've already checked this cave, its empty!"? In particular, is this frequently done?
This paper is great: How not to prove the Poincare Conjecture by John Stallings (now deceased unfortunately.) A great mathematician with a great sense of humor.
Bibliographic info:
Stallings, John, How not to prove the Poincaré conjecture. Topology Seminar, Wisconsin, 1965, 83–88, Ann. of Math. Stud., 60, Princeton Univ. Press, Princeton, NJ, 1966.