Look at the design values for log beams vs timber beams. I'll have to find where I stashed the log code but the log beams have higher base design values if <1/10th the diameter is skimmed off the top. The "chord" of fibers is largely intact vs running out of a squared timber.
Eric Sloane commented that it looked like old time carpenters thought that removing knots strengthened timbers, they had hewed them out of many joists, even though this might not be helping in our view.
