I asked because I was curious - I'm finding that for me it has to be fairly short sessions, 1-2 hours, then I get tired and need a break. I may or may not go back later. I think one of the most important lessons I've learned is knowing when to stop - it's when I don't that disaster strikes!
I've just bought a Featherweight, and am planning to have 2 projects on the go now: there's a big backlog of quilting to be done, but I think I'll use the second machine to do some piecing to give me a break from that. In fact the need to stop fairly frequently may be because I'm mostly doing quilting, which I find needs a lot of concentration, not to mention the physical effort of hauling a quilt through a standard-sized machine!