I agree with Stephen, in that the crew is typically more than able, and willing, to handle the mainsheet upwind for me. Aside from leverage issues, my crew can focus more on trimming the sails correctly, leaving me to figure the shortest distance to A mark, as well as seeing what wind the other boats are in (header or lift, gust or lull, etc.). Should a cross with another boat be near, the crew certainly can understand my "we're going to duck/carry this guy" and adjust accordingly.

The other thing is balance. Holding the mainsheet keeps the crew (and therefore my skinny butt) on the hull in cases where waves try to stop the leeward hull.

Off the wind with no spin (tight reaching), the crew stays with the mainsheet and downhaul, while I keep the traveler and jib sheet (both of which require minimal adjusting). As Mary says, it keeps my head out of the boat more and I can pick my line better.

Off the wind with spin (borad reach), the mainsheet's cleated. I play the traveler and jib, while the crew focuses on the spin. Should the crew ever take his/her eyes off that thing, I will personally gouge them out, as it takes about 0.0000001 seconds for that thing to collapse or stall. As mentioned before, neither the traveler nor the jib need much adjusting.

I DON'T have an autotacker, so jibes get dicey occasionally, but a little planning and communication allow all the lines to get clear while turning.

And we dump the boat occasionally, but it has little to do with the main being cleated (this only complicates the issue). Usually, the dump is the direct result of that pesky "loose nut on the tiller".... Which, unfortunately, isn't covered under the warranty!

Jay