Supposing there is a bit of information that is relevant to some or all of your products. Then consider that the information might change from time to time. Perhaps you have 100 products out of 150 that all come with a 30 day money back guarantee. You could enter that guarantee information into the product description. But what if you then change it to a 60 day guarantee? Even worse, what if some products changed to 60 days, some stayed the same, and some needed the guarantee removed?
Custom fields were designed for such nightmares. What we will do in this recipe is create a simple text custom field for 30 days money back guarantee.
Then you will be able to add or remove a custom field or edit the custom field using the information gained in this recipe and, as if by magic, all the products with that custom field will change too.