[adouglas]

If the tank is left open to vent, you won't get condensation. An empty or near-empty tank, sealed, could still have moisture in it. If you wash a drinking glass and leave it upside down to dry, it'll say wet inside for a long time because the moist, trapped air has nowhere to go. Same idea.

A full tank minimizes the amount of air available to hold moisture. I'm a private pilot and standard practice is to fill the tanks after landing for the same reason. Keeps condensation from happening. Water in your fuel is a Bad Thing... and part of every preflight is to drain a little fuel out of each tank as well as the carb to check for/eliminate any trapped water.

Leaving the tank open to the atmosphere implies draining the system completely, of course. Personally I don't think it's necessary for winter storage provided you have a full tank of stabilized fuel.

I like the convenience. Come spring, all I have to do is air up the tires, unplug the tender, wheel it outside and go. Always fires right up.

If I were storing a bike for a very long time (vs. just a few months over the winter) I would drain the whole thing... plus do some extra prep like spray fogging oil in the cylinders.