When should I use a UPC or EAN number for my products?

You need to use EAN UPC codes when you have a product to sell. you need to have a code Number for each variation of the product. You don’t need to use different Number for same item even its in 100’s.

In fact you need these codes to sell your products at eBay, Amazon or any other marketplace or high street shops as unique identifier which differenciate your product from others as we don’t know how many other brands are also selling similar items so this is the easiest way to find the identical item.