Retool Workflows is a feature within Retool that allows developers to automate recurring tasks and backend processes that typically occur outside a user interface, enhancing efficiency and productivity for startups. The described use case, "Big Fish Swimming," demonstrates how Retool Workflows can be utilized to monitor new customer signups, particularly targeting larger companies by integrating with the Clearbit API to obtain company size data. When a new signup occurs, a webhook triggers a workflow that fetches information from Clearbit, and based on the company size, sends a Slack notification to the sales team for personalized outreach if the company is large. Otherwise, it triggers an automated thank you email with a promo code for smaller companies. This workflow exemplifies how startups can leverage Retool Workflows to optimize customer engagement strategies by automating decision-making processes based on market data.