Prerequisite for any organisation is to be selfsustainable, so you can reach your goal without getting bankrupt. You need money to survive, generate revenue. The way of generating revenue is called a businessmodel.

You can have more that one business model in your internet business and one can be more important than the other. For e-commerce, a merchant model is the main model, but making combinations with other models are certainly possible.

On the internet there are new possibilies for making money, for example those only based on generating visitors.

What is good about naming the businessmodels it that you get more aware on the moneypart of the business, although the money is of course secundary to serving your customers and reaching your mission.

A  great site  to read about the topic is from a professor Rappa.
He mentiones on his site brokerage, advertising, infomediary, merchant, manufacturer, affiliate, community, subscription and utility as business models and for each of these groups he has defined variations.

Selecting the right model(s) for your internet business is part of the strategy you must use to become a winner.

Understanding the way you will make money, will help you later on in identifying part of the key area's of the business. It can give you a clue on how you can make more profit, and what processes are important in this aspect. It will also help you identify important partners for your success, it defines possible relationships you must establish to make the model work.

Also a word of warning: the model or combinations you choose should not be annoying to your customers, otherwise your profit will not be long lasting.