You walk into a retail shop, and see some of their products are on sale. The reason you notice this is because you see the sale price next to the normal retail price. This simple visual indicator is an extremely effective way to get customers excited about a sale your shop is having and start making purchases!
Having a sale in a Shopify shop without Simple Sale is not easy. You could manually change all of your prices, but this would take a long time and the possibility for error is large. Alternatively you could create a coupon and advertise it to your customers, but they would have to remember to input it when they checkout. Both situations are not ideal.
Simple Sale works by temporarily putting the retail price for a product in the compare at field and then puts the sale price into the normal price field. Simple Sale takes care of all of the calculations for you. Just enter a sale percentage, choose a collection or your entire shop and click the start sale button!