I don't know anyone going with 1/2" as mainsheet for the simple reason it won't fit in most blocks.
If you're using 2.25" (57mm) blocks, 3/8" fits good, 7/16" doesn't. If you've got 3" (75mm) blocks, 7/16" fits good, 1/2" doesn't (at least not very well).
The advantage of smaller line is that when you let go, it feeds out faster - assuming your tackle is in good shape. The advantage of bigger line is ease of sheeting in - more to hold on to. But smaller line is cheaper and plenty strong enough for the applications we have
And I'm "The Dog"... Have been for years. But I guess there's probably room for two if I have to share.
Cheers,
Brian C