Companies you set up in Companies and Contacts are used across three features.

On the Repair Estimator, the Bid Manager widget lets you track contractor bids and assign each bid to a specific contractor.

Assign responsibilities to companies for schedule tasks, so you can coordinate each company's start and completion dates for major renovation items.

Assign expenses to specific companies so you can track how much you have paid each one across your projects. This is also what powers the Vendor 1099 Report.

Read the full article: How is the Company and Contact info used throughout the software?