1. I can leave within a greater time tolerance, there is no absolute "take off" time.
2. I don't have to be in "public" mode the whole time. No matter how I try to relax, if there are people around me within a few feet (inches?) I can't really relax.
3. I can put stuff in my car that doesn't fit nicely in a piece of luggage. I like to just throw my tennis shoes in the back seat, because they take up so much frigging room in a suitcase (size 14). Also, I'm more likely to bring a little food to put in the hotel fridge to save on some breakfasts or dinners at my destination.
4. Easier access to snacks and stuff. I usually put a cooler in the back seat accessible to me while driving. It sounds dangerous but it's really not (!).
5. Being able to drive my own car at my destination (usually from hotel to job site and back). I save on the rental car, of course, plus just the comfort of driving the car I'm used to.
6. Can charge mileage to my company. Even though I am self-employed, it feels like free money when I charge 36.5 cents/mile to myself.
7. The time lag on each end is dramatically shorter. For instance, for me to drive from Columbus Ohio to Detroit takes just over three hours. A jet can fly there in 40 minutes. However, if you count getting to the airport 1.5 hours early, parking, check-in, waiting on the runway, waiting for your baggage coming off the plane, and getting a rental car, that actually takes over four hours. So driving is quicker and a lot less headache.
8. No weather delays. Rain, thunderstorms or hail are very unlikely to stop me from driving anywhere. Snow could possibly delay me if it was bad enough but it would delay the airports long before it would be bad for driving.
9. Not so likely to catch colds. With the recycled air on airplanes, I often catch colds. In my car, the only recycled air I'm breathing is my own (which is bad enough).