Sales can generally get you a good deal on something, but the people who set up the sales understand how you shop and how to ensure they make as much money from you whether you shop in the sale or at normal times. There's a number of strategies, but no matter how it might seem the sale is not for you, it's for them.
I have generally not paid much attention to sales. If one is on when you are shopping then sure, take advantage of it. But don't factor a sale into your expectations. Plan out what you want, and if on the day you can get better value a slightly different way then fine, but if not you planned something you would be very happy with.