There are numerous situations, where drawing your gun while sitting in a vehicle may save your life one day, including car jacking and road rage incidents. While the vehicle itself may allow you to escape the situation or to use it as a weapon, in many circumstances drawing your gun and shooting through the windshield or a side door/window may be necessary. We had two recent car jacking incidents in my area (West Knoxville, TN).
The same thing goes for sitting in a restaurant (fine dining or fast food). If an armed robber comes in to the restaurant, you are certainly not going to stand up from your table in order to draw. We had several recent restaurant robberies as well.
These types of unusual holsters are typically heavily marketed to those that have zero training. There are other issues with such holsters that make them impractical, including a more complicated one-handed draw.