Merge's Unified API simplifies the process of building and maintaining integrations with various systems by providing a single data model for syncing and normalizing data across platforms like CRM, ATS, and HRIS systems. This API allows developers to perform CRUD operations and set up webhooks to automate tasks such as user deprovisioning, reducing manual effort and time consumption. Specifically, using Merge with an HRIS system like Humaans, developers can automate the revocation of access privileges when an employee leaves an organization by setting up a webhook that notifies internal systems of such changes. The process involves creating a link between Merge and the desired HRIS, setting up a Python-based development environment using Flask to handle webhook requests, and using tools like ngrok to test the integration. Merge's platform supports over a hundred integrations, streamlining the development of complex integration projects and allowing developers to focus on building their applications.