Generally, when a foreign client starts a new business in the U.S., we form a new corporation for both business and legal reasons. Recently, however, I had an interesting experience helping a foreign client set up a branch office without forming a new legal entity.
The client acknowledged the benefits of a new corporation. However, procedural issues for the client (located in Southeast Asia), would result in the necessary approvals taking too long. As a result, the client asked that I first provide help setting up a branch office in Silicon Valley. That branch office later would be used by a new California corporation that we would form.