I like to fly between 6000 and 9000 feet. It’s high enough to be above most general aviation traffic, it is cold enough that it is not sweltering hot in the cockpit, but not so high as to require supplemental oxygen. My airplane’s engine appears to be perfectly happy at those altitudes.

I regularly fly above forests and mountains. I just love the beautiful rugged landscape. In those parts, flying higher provides a safe margin above mountain peaks.

Furthermore, should I experience an engine failure, flying higher means having more time to troubleshoot the problem, prepare for an emergency landing, identify a suitable landing spot, and glide to it.

Many pilots fly low in order to avoid controlled airspace. I guess they don’t like interacting with ATC, or might be intimidatd by it. Personally I prefer to climb up in the terminal airspace and request VFR flight following. ATC is not there to scald pilots at every little mistake they make, they are there to help us navigate to the airspace they control and help us get to our destination safely.

The things that keep me flying lower? Cloud cover of course, and sometimes haze. I have found that a good pair of polarizing sunglasses help tremendously with haze.