Typically, ribbon buttons are used to quick-launch workflows, execute calculations/transformations, perform complex on-demand validations, and much more. Custom ribbon buttons are also used to redirect users to external locations when integrating Dynamics 365 with other systems.

Although the ribbon editor is a great tool, sometimes unexpected behavior can occur, which would require you to take a look at the underlying XML for debugging purposes and manual edits. In case you want to learn how to edit the ribbon manually, refer to the MSDN article at https://msdn.microsoft.com/en-us/library/gg309639.aspx.