When modifying a Microsoft Dynamics 365 solution, you may require functionality that is portable and can be triggered in multiple circumstances. For example, running a rollup field calculation job, which is able to be done from SDK messages, but otherwise cannot be triggered manually out-of-the-box. In this instance, you may require a plugin or a custom workflow activity that calls the SDK message and runs the job. However, if you want to be able to run this from multiple places, a plugin may be more appropriate.
Custom actions were added in Microsoft Dynamics CRM 2013, and provide a fantastic point against which to register plugins. Once actions have been created, it is possible to register a plugin against their schema name, which acts like a custom SDK message that is fired whenever the action is called.
Custom actions can provide the target for a plugin as well as pass values to plugins. This is done by setting input parameters for the custom action and then accessing these using from the plugin execution context.
To register a Plugin against a Custom Action: