A button is a type of field that you can add to a form. The main reason to add a button is for workflow navigation to other forms or to enable the form to pull data into it through the use of the new button.
When adding a new button, evaluate the functionality provided by the button and determine the most appropriate place to put the button on an existing view. If the functionality will be used infrequently, you can add a link in the navigation bar instead of adding a button. The navigation bar enables you to add the functionality without cluttering the view itself.