This is probably as much an engineering question as it is a design question but I would like some input from a design standpoint as well. I have noticed in all the books I have read so far and the gallery's I have seen that most timber members are rectilinear and of uniform width. The rare exceptions being curved braces, arches and gunstock posts.

Why are tapered beams/posts seldom seen or used? It seems to me that much is being lost by keeping boxy timbers especially when it comes to rafter and truss design in efficiency, strength and visual perspective and interest. Are there any timberframe designers out there who have specialized in tapered members? In terms of weight distrubution this arrangement should yield superior results as well as giving a feel and illusion of greater height because of the diminishing width as it rises. Smaller logs could be more efficiently utilized by using natural tapers yielding a savings in lumber and overall cost.

I recognize the obvious answer would be that it is much more demanding to cut timbers that are not square when perpendicular. I think the payoff may be worth it if for nothing other than aesthetics.

I like this question.
Last year we cut an octagon frame and tapered the principal rafters. I wish i had done more tapering, especially the principal posts.
I did not feel that working with the tapered pieces was more time consuming, the snapline joinery i use most of the time seems to translate easily. We only tapered in width, however and tapering both width and hieght would mean some stacking challenges...

Our engineer had no trouble working with the tapered timber...