We saw some in DS9 - and they achieved nothing against capital ships.
Apparently, by the Trek rules of combat, small spacecraft are analogous to small boats while large spacecraft are analogous to large ships, in Hornblowerish terms: small craft do not have access to "missiles" or "torpedoes", but merely to the same type of weapons that the capital ships have, only smaller and weaker. Furthermore, small craft appear slower than large ships at warp, have weaker shields, and do not gain any advantage from their subilght maneuverability because anti-fighter fire from the capital ships is 100% accurate even against wildly maneuvering targets.
That's the tech side. Of course, it is merely the necessary result of the more important side: the dramatic aspect. Trek heroes fly capital ships, so capital ships are better than anything else. And that in turn is originally the result of real-world limitations: effects technology (and other cinematographic realities) at the time of TOS would not have allowed for a fightercraft-based show. Even TNG would have been hard pressed to achieve anything even remotely like Star Wars, and would at best have repeated the crappiness of the original Galactica. Two fighter effects per season, recycled over and over, would grow tedious even faster than the recycled flyby shots of the hero ship.
Okay, so now the effects wizards can do fighters. Should they? The imaginary tech rules can always be bent or broken, e.g. by referring to technological breakthroughs in the Trek universe that suddenly make fighters a viable weapon after all. But there is another kind of inertia there. Trek has always been about a bunch of actors exchanging lines with Shakespearean precision in a cardboard-walled set. To go from there to a setting where solo actors exchange wit between computer-generated cockpits would be a massive dramatic change, and quite possibly the only way to actually do "Trek that is not Trek".
Timo Saloniemi