Bend deduction vs. Bend Allowance vs. K-factor

To all you sheet metal people out there i have a question. I would like to know which feature you use and why? Bend deduction, bend allowance and k-factor. Depending on which one you choose, it changes the flat pattern. For example, which one should be used for 90 degree bends compared to bends that are not 90 degrees.

thanks in advance

SolidworksSheet Metal