The Netlify Build Plugin allows developers to automate tasks by writing custom scripts that are invoked at specific points during the build process. These plugins can help manage notifications, kick off events, and incorporate various purposes into workflows. To write a plugin, developers need to create a JavaScript object that hooks into lifecycle events such as `onInit`, `onPreBuild`, `onBuild`, `onPostBuild`, `onSuccess`, and `onError`. The simplest implementation would hook into the `onEnd` event to send notifications after a build has completed. Plugins can also be published on NPM, installed via NPM or Yarn, and referenced in Netlify's configuration files. This automation can help developers increase productivity by streamlining tasks and automating repetitive workflows.