Price Settings allows you to choose your options for what happens when change the Unit Cost of a Product regarding Price, Margin, and Markup. Choose wisely.
Note: If you are using Use Tax on a Product and have also chosen to "Include Use Tax in margin/markup calculations" in your Tax Settings, your option for Price Settings will be ignored for those Products. When Use Tax is added/changed on a Product SI will always recalculate the margin/markup and maintain the Unit Price.