99.9% of the time when not below, I and my family wear our life preservers. Once in a great while, if it is glass and hot, I will take mine off and let anyone else take theirs off if they are sitting completely in the cockpit (My boat is a center-cockpit boat). However, if anyone is outside of the cockpit, they have the preserver on. I leave it up to adult guests to do what they wish (I overrule if the weather or traffic becomes too much) but we insist children of guests wear them.
If we are in our dinghy just motoring around the marina at idle speed, we don't have to wear them. If we decide to take the dinghy out on Lake Michigan, we all wear them and I attach the kill lanyard to the vest.
"To reach the port of heaven, we must sail sometimes with the wind and sometimes against it - but we must sail, and not drift, nor lie at anchor.”
- Oliver Wendel Holmes