Depends on what "truth" you're looking for. Ursula Le Guin, both fantasist and s.f. writer like so many of the older generations, has said her profession is lying to tell the truth (paraphrase), and she's not the first to make that assertion.
If you're looking for facts, fiction is not useful. If you're looking for more insight into the workings of the human mind, of how various people act and think, and what it means to be human, then fiction is one of the places to search, lies and all.
Randy M.