A Company record includes all the Contacts that are assigned to it, as well as other details that can help you quickly determine if leads and Opportunities can be generated from those Contacts. Here are a few of the fields for a Company:
Contacts that are part of the company
Client Solutions Roadmap
Interacting with a Company
Companies provide a high-level overview that really helps when prospecting Contacts. For example, you can easily see how many Opportunities each Company has generated for you. You can also use Company records to coordinate Salespeople so you don't end up with two different Salespeople going after the same Opportunities at the same Company.