It isn't that the game doesn't really update your position until you land so much as the server always is behind your client in determining your position (where you see yourself isn't where the server sees you until shortly after). Running out of fire and jumping out of fire (provided you are moving horizontally at the same speed) will remove you at the same time on the server side.
So where does jumping actually create a difference? One example would be Lava. Jumping in lava behaves differently than simply swimming through it. Swimming through it your next tick is based off of the time the last tick occurred. Jumping in it because you exit and reenter you are actually changing the frequency of the ticks. Some mechanics other than lava could function this same way, where jumping causes you to temporarily lose the effect and then regain it, lava is just a example just about everyone should be familiar with.
Because moving out of bad you don't gain speed by jumping there is no benefit to it under the majority of circumstances. For running out of bad it is ill-advised to be jumping out of it typically because once you jump you commit yourself to a given direction and can't adjust if say for example fire that spreads or tracks a particular player (if they dart off in the same direction you want to change direction).
When jumping is good (besides specific mechanics)? The tanking example is one such case where jumping is helpful. When moving straight through a boss you can jump forward at full speed and turn mid air when you are on the other side of the boss to minimize the time your back is exposed to the boss. Additionally, any encounter in which there is collapsing and spreading, or significant movement where DPS is not facing the target they want to jump while moving, turn mid air to use an instant, and turn back before they land. As an example, on Morchok during the black blood phase the DPS can jump and cast an instant on the boss mid air and land continuing to run away.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.