The main advantage of using different corporations or entities is liability protection. If different businesses are set up in different corporations and one of the businesses has legal troubles, it should not affect the others because each is considered a separate legal entity. Suppose Jim Jones owns a trucking business that operates locally in several different states. If he incorporates the businesses in each state as separate entities, he has provided some insulation to the other businesses. However, liability protection is not absolute or automatic and often depends on the circumstances of each case.
The downside of forming more entities to conduct business is that each entity must keep its own records and file its tax returns. This, in turn, increases the amount of record keeping and probably increases your accounting and tax filing costs.