The descent stabilizer prevented the turbolift from plunging down when descending by counteracting the downward pull of gravity. It also prevented any occupants in the turbolift from being pinned to the roof in a descent. If the descent stabilizers were to go offline mid-descent, the g-forces (presumably created by artificial gravity while a starship was in space) would force the occupants to the roof. However, when the descent stabilizers were reactivated, as described by Neelix, it would prevent anyone stuck on the roof from crashing down to the floor of the turbolift, if the turbolift came to a sudden halt after speeding downwards in free-fall.
When telling the children on Voyager a ghost story in 2377, Neelix related an incident where Chakotay was stuck in a turbolift that fell eleven decks before the stabilizers re-activated. (VOY: "The Haunting of Deck Twelve")