Pdqdl, Ouch!
Most the time I try to use both hands but sometimes use one hand if I think the other would be better for useing as balance by holding on to another branch. So it just depends but mostly I try to disipline myself to use both hands. Once a nieghbor walked over and asked if I could cut down a limb out of his Silver Maple. I had been drinking and had a pretty good buzz but not overly drunk at the moment so I said sure and went over to house, climbed up and cut the branch off.
To further my use of poor judgment I used one hand on the saw and somehow placed my other hand in the cutting path. Somehow I ended up tearing off my middle fingernail and leaving a little gash on my middle finger. Luckily I was buzzed enough not to feel it too bad, and when I got back down we drank some more so it didn't ruin my night other then feeling pretty stupid. Since then I have made it a personally policy not to drink and climb. Never did figure out how I put my finger in the saw path