Costs – economies of scale in the long run increase the productive capacity of the business whilst also leading to lower average costs
Market share
Risk
Managerial – motivational theories of the firm predict that business expansion might be accelerated by the demands of senior and middle managers whose objectives differ from major shareholders
Expansion from outside the business mostly through mergers (where two company's work together usually because both are starting to become unsuccessful) and takeovers (original company no longer exists)
Eliminating duplicated functions and services (e.g. combining the two accounting departments)
Getting better deals from suppliers which might be possible if combining two businesses gives them improved bargaining power
Higher productivity and efficiency from shared assets; can capacity utilisation of the combined businesses be improved, perhaps by closing down spare capacity
A merger can be seen as a decision made by two businesses that are broadly "equal" in terms of factors such as size, scale of operations, customers etc.