>>14
That's not really what the sage function was originally intended for, but that's how it has been used. This behavior is mostly confined to 4chan. On imageboards and textboards outside of 4chan I see what is called "polite sage-ing" where someone will make a contribution but use sage as to free up room on the front page for newer threads. Some have said that they use it because they feel that their comment, while helpful and informative, does not need an age (or bump) of the thread in order to be posted or seen.