I was leading a rope of 2 and just about at the summit of Rainier, when the dumbshit behind me fell off a snow bridge into a deep crevasse. What had been up to then a pleasant climb, then became a very serious and difficult matter as I was dragged a bit before being able to stop, with a partner dangling in the void. So ever since that incident, I really prefer 3 on a rope on a glacier. Do I always travel with 3? Of course not, I am willing to take risk, and sometimes all I can find is 1 partner. So there is no real answer to your question, as we all take risks, but as I am sure you know, 3 is the safest way to go, and you won't regret adding that third person.