I don't have one, but I need to get one. Keeps the cross hairs level, if they arent some of the elevation that has been dailed in is now throwing your round to the right or left (depending on which way your canted) and is now longing aimed high enough to conteract gravity, so the round is going to be off target horizontally and low. Plus, any adjustments wont be accurate. Say you canted right and shot low right. So you turn your scope up and left. Now that really will move it further right and up for elevation and further left and up for the windage adjustment, if your cant is exactly the same on the next shot.
I used to have a stock that flexed so bad when on the bipod that I could sight it in on a rest, switch to the bipod and be eight inches off at 100 yards.