Businesses, subcontractors or suppliers you do business with on your projects. For example Home Depot, your general contractors, painters, real estate broker, lender and title company.

Employees at a company, or any individual you need to store in your database. A potential buyer, a home seller, or anyone else.

Companies can be assigned to Project Schedule tasks and to expenses. Contacts cannot. That is the practical reason to enter a business as a Company rather than a Contact.

Read the full article: What's the difference between a Company and a Contact?