not necessarily.
you can need it to finalize what you just slowed down with your handgun, for instance. The pistol can "buy" the time needed to get to a longarm and unfold the stock, or possibly even assemble that longarm, even. This is especially true if it's something fast, to assemble like an AR 15.
You can need it to finish off a critter that's been hit by a car, or one that is rabid and trying to reach you(while you are in the car). On your own property, that of a friend, or on BLM land, in season, you might need it to harvest $3000 worth of elk meat, or even a moose, which can be twice as much meat. You can need it to shoot up a dog pack or rabid critter that's chasing livestock. One chuck can eat $1000 worth of your soybeans, or squirrels, rabbits,armadillos, prairie poodles or deer that are tearing the hell out of some expensive plants. Every female rabbit, etc, that you don't kill can raise a dozen more that year, and some of her young will have more.. Ditto prairie dogs.
In some locales, the gun must be disassembled to be legal in the vehicle, especially if it's not locked in a trunk. You might have a chase scene, never know how it might go down. I'd never willingly be without a pistol, but the right longarm (like an SKS) can add a lot of potential. But you may well need to hide it in a place-way that requires that the longarm be disassembled.Not everyone drives a van, SUV, or pickup.
Deer can kill you pretty easily, if you hit one with your car, or reflexively "ditch" to avoid one. One rabbit, on one night, cleaned out all of my gf's snowpeas one year. She shot it herself the next evening (pellet rifle) and we ate it.