If you can, it is far more efficient to chop in from opposing sides.

For simplicity, consider a piece of square timber that is 3 inches by 3 inches. You make a notch on one face, whose sides descend at 45 degrees to meet at the other face of the timber. The sides of the notch are 4.25 inches, meaning your notch's cross sectional area is 9 square inches, times the depth of the timber (3), is 27 cubic inches of material you had to chop out.

Now chop in from both sides, with a notch descending at 45 degrees and meeting in the middle. The sides of the notch are 2.12 inches long. The cross-sectional area of the notch is 2.25 inches, times the depth of the timber, gives a volume of 6.75 cubic inches per notch, times two notches, is 13.5 cubic inches of wood removed in total.

13.5 versus 27. Exactly half as much work. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Of course this is only possible if it's something you can easily roll or step to the other side of.