I have read that the way blades are made there is a slight burr on the right side so blades tend to drift in that direction. Altho I cut in both directions when necessary, I try and cut so the blade will drift into a waste area. It's easy to go back and "shave" the excess to get back to the line, but kinda hard to put wood back on. Yeah! I know!! No one will notice when you take the pattern off, but if a line is supposed to be straight, to me, at least, it shows up like a sore thumb.
Pete