Snippet injection allows developers to add small temporary features to their Netlify sites without modifying the source code, making it easier for team members to collaborate and manage changes. By navigating to the Post processing section in Netlify settings, users can select where to inject the code, choose a name for the script, and paste HTML or JavaScript snippets to achieve specific functionality. This feature enables developers to quickly add or remove features without needing to be familiar with the underlying codebase, promoting flexibility and collaboration.