The travel utility of a GA airplane is shaped like a donut, and the size of that donut depends on the airplane you have and what the roads are like where you live. The closest airport to me, KRYY, is a minimum of 25 minutes away, 30 minutes is more typical at non-rush hour. I would be renting, so I'd have to check in with the office, then preflight, start up,and get a clearance. That's got to be a minimum of an hour total, and in that hour the car would be at least 50 miles down the road. Figure 15 minutes to get out of terminal area at a reduced speed, but let's ignore that since the airplane can go point to point and the car has to go a little more indirectly. I'm not rich, so I'm figuring 110 knots in a Skyhawk,which is about 50 mph better than the car does.
So, at the end of the first hour the car is way ahead, and at the end of the second hour the airplane has caught up. Does that mean the airplane is faster on any trip that's more than two hours in the air? Yes, provided your destination is at an airport. Since it almost never is, now you have to consider ground transportation at the other end. Figure 10 minutes to taxi and get tied down, a few more minutes to arrange things with the FBO, some more time to get ground transportation, and more yet to get to that destination, and it's now gotten to where that car ride has to be more than three hours before the airplane is faster. I did a little planning on a trip to Nashville a few hours ago, which is about 240 miles away, and still found that the car was at least as fast. So that's the inner edge of my donut.
Now think about the outer edge of the donut. The nearest airline airport to me is ATL. I would allow an hour to get to the airport and 1:15 before departure, then taxi and a wait, and finally get airborne. The Skyhawk will probably be 180 miles closer to its destination at that time, but since the Boeing/Airbus is traveling so much faster, it has caught up in less than 45 minutes, so the outer edge of my donut is around 450 miles.
Real world example: I live in north metro Atlanta, my mother lives in Brooksville, Florida. She's recently given up driving, so I'm going to pick up her car, get it cleaned up and get it sold for her. It's 445 SM from here to there. It's fairly direct, the savings in air miles is not much. I can routinely make the trip in 7 hours plus a meal break, if traffic is light I can make it in 6.5 hours. I'm flying commercially next week, I'll be leaving home at 5:15 to make a 7:35 flight, which arrives at TPA at 9:00. I should be at the assisted living place where she lives by 10:15. If I were flying that Skyhawk, the closest airport is KBKV. I'd allow an hour to get to KRYY, check in, and preflight, 15 minutes to get taxied and out of the terminal area, 3:30 enroute if there's no wind, another 15 minutes to descend, land, and taxi, and 45 minutes to get tied down, get Enterprise to come and get me and to get to the ALF. That's 5:45 all in, and the airliner was faster.
Normally I would drive, and I see no reason to change that. If you have access to a faster, all weather traveling machine, then your donut is much bigger. If you have that $50 per hour Cessna 150 that was mentioned in an earlier thread, you may have no donut at all.
