LeftAndMainis more of a lower-level API and not often required due to the existence of
ModelAdmin. However if you wanted to create a custom user interface that did not necessarily require the functionality of
ModelAdminin the administration panel for your module, than
LeftAndMainis where you would want to start.
The easiest way to create a RESTful API in Grails is to expose a domain class as a REST resource. This can be done by adding the grails.rest.Resource transformation to any domain class.
It is often useful to present a first-run experience to new users of your App. This could be for any number of reasons, such as prompting them to sign in (if required for your situation), explaining how to use the App, or simply informing them of new features in an update (as Notes, Photos and Music do in iOS11).