As long as there are top handled saws to buy the practice of one handing a saw is not going to go away. I sit on the fence on this issue, this is the main reason I switched to a rear handle for climbing so I don't one hand a saw while climbing. Working out of a bucket I do a lot of one hand cut and pitch of small limbs, you have a lot more stable and positioning options than you do while climbing, and you can choose your cuts better than you can while climbing.
You can't have control 100% of the time when you one hand a saw , sooner or later you will misjudge the situation, the work piece might be heavier than you think, tangled up bad with a neighboring limb, will put more leverage on a cut than what you might be ready for, this list could go on and on. What appeals to you the most if things don't go quite right and that saw is going nine ninety and your holding on to that piece of wood. How about a cut wrist with some tendons cut, or a chewed up forearm or leg, or better yet, cut your life support system and fall out of a tree. These are the risks you take one handing a saw, QUESTION, Is it worth it yes or no.
Not one handing a saw will improve your saw cutting skills. Makes you better at Z type or snap cuts so you can use two hands to break the piece off and manipulate it easier, notch and hinge, under and over cutting for free falling limbs. It doesn't take that much extra to carry a small short rope on your saddle and use like a choker, beats one handed saw cuts. With the improvement in the handsaws we have today, one handing a chain saw shouldn't have to be done so much.
Like Mb said, it will catch up to as you get older, I think MB has shoulder problems, mine is more in the lower back, weight being transfered from arm to lower back from hanging on to heavy limbs one handing a saw while working out of a bucket, all because I thought I was being faster than not setting and using a rope. Nope not
Larry