Tire clearance is a top ten discussion item with the Rivendell set. How big a tire can you fit on frame xyz? The recommended range for the A Homer Hilsen goes up to 43mm. My A Homer Hilsen is now wearing a pair of Ritchey Speedmax Comp 700x40 cyclocross tires. The actual measured width is more like 36mm on narrowish road rims. Still a lot of tire though. I don't know of a beefier cyclocross tire that is not a 29er tire...if only.
Even better, there is still room to keep the SKS P45 fenders on. This set up may not be for those who are fender worriers; those who lose sleep over thoughts of junk jamming the tire in the fender. I could probably adjust the fenders a bit to get more space, but it's just fine the way it is. Without fenders, the frame could easily swallow a much larger tire.
I wouldn't use these tires all the time because moderate slick tires are more than adequate for a wide range of conditions, but for commuting in the fall fat knobby tires make sense. Thick layers of leaves cover rocks and holes and make it difficult to avoid the nastier parts of roads and bike trails. Having a little more cushion and grip between me and the ground makes that difficulty quite manageable. I think they give the bike a nice sturdy appearance too.