First of all, there are some who would say that a person who buys an existing business is not an entrepreneur. An entrepreneur is sometimes defined as someone who creates a new business.
That said, the major advantage to the person who buys an existing business is that they do not have to build up the business’s clientele from nothing. For example, if you want open a completely new restaurant, you have to make people aware of your restaurant and convince them to give it a try. If you buy an existing restaurant, you have a base of customers who are already aware of the restaurant. Getting them to keep coming is less difficult than attracting new customers to an entirely new restaurant.