Before the products can be setup in ADempiere, you should have a good understanding of how the product information is used to generate performance data so that you can generate the reports required to manage your operations. The first question is whether you require a product at all. Consider a bill for electricity. It would be unusual to verify that the quantity of electricity provides was actually received before the bill was paid. In such a simple case, the accounting for the electricity could be made using a Charge with no product definition involved and no process beyond the invoice and payment. However, if it was important to track the amount of electricity consumed and the cost of the electricity over time, creating a product for it would be helpful.