Subsidiaries can be formed in different ways and for various reasons. A corporation can form a subsidiary either by purchasing a controlling interest in an existing company or by creating the company itself. When a corporation acquires an existing company, forming a subsidiary can be preferable to a merger because the parent corporation can acquire a controlling interest with a smaller investment than a merger would require. In addition, the approval of the stockholders of the acquired firm is not required as it would be in the case of a merger.
When a company is purchased, the parent corporation may determine that the acquired company's name recognition in the market merits making it a subsidiary rather than merging it with the parent. A subsidiary may also produce goods or services that are completely different from those produced by the parent corporation. In that case it would not make sense to merge the operations.