The Gmail API provides a streamlined opportunity for applications and frameworks to communicate with each other, allowing for automation of email sending processes. With PHP, developers can leverage this API to send emails securely and efficiently, utilizing features such as OAuth 2.0 authentication and base64url encoded strings. By setting up the project, choosing a guide and API library, accessing Gmail credentials, creating an email draft, and sending the email, developers can effectively use the Gmail API with PHP to automate their email sending processes.