Companies represent the organizations behind your deals — accounts, prospects, partners. Keeping them tidy gives every deal the right context.
A company ties together the deals and contacts related to it, so you can see the whole relationship in one place. Assigning an owner makes it clear who's responsible for the account, and custom fields let you capture the details specific to how you sell.
Tip: because CRM shares the contact database, the people at a company are the same contacts your marketing and support teams already work with.