In "Knight Rider" (the original, not the insipid remake), Michael Knight never wore a seatbelt, as you wanted the fast past action of him being able to jump into the car and speed off or get out quickly, etc. When it became a concern that kids were watching this and seeing him not wearing a seatbelt, the producers invented a new feature of KITT called the "passive laser restraint system."
How it worked was never explained. But from the beginning of season 3 onward, anytime they were going into a high speed chase, we'd see Michael turning it on, presumably protecting him without the need for seatbelts.
Logically, the Enterprise, with artificial gravity and inertial dampeners, should be able to do the same thing. Dramatically, of course, we know it's because they want to be able to show people flying around the bridge following a phaser hit. But it makes no logical sense.