How does the difficulty of a shot vary with cut angle?
The following analysis (which includes several useful graphs) shows how the margin for error varies with both shot distance and cut angle:
Also, the effective size of the pocket varies with angle and speed. For more info, see: pocket “size” and “center”
All of this stuff obviously depends on table pocket geometry and facing conditions.
As proved on the last page of TP 3.4, for a straight shot, shot difficulty is directly related to the product of the distances between the CB & OB and the OB & pocket. A straight shot is most difficult when the OB is exactly halfway between the CB and the pocket.
An article that discusses how the angle increases the difficulty of a shot (which is to say, decreases the allowed error), is at: http://www.sfbilliards.com/articles/1994.pdf (April)
The article includes a simple graphical way to see how much the cut angle increases the difficulty over a straight-in shot of the same length.