This is an issue that I have been thinking over for a long time. Being tethered to the boat can be worse than not being tethered. I hate the tether as it restricts my movement so much. I have jack
lines, and an expanding tehter, but I find it hurts me more than it helps me. My new rule. In reasonable calm conditions, singlehanded - no tether. Rough conditions I tether. Short handed - like one or two competant crew -no tether except in extreme conditions.
I do wear my inflatable life jacket on deck whenever singlehanding and in rough conditions with crew or in cold water.
I have found tethers to restrict one''s ability to make quick on deck manuevers. My present thinking is, when singlehanding, once you go over your done - tethered or not.