A portlet’s Display Settings (Options → Configuration → Setup → Display Settings) let you customize its display. They come built in with Liferay, so you don’t have to do anything special to enable them for your custom portlets. But what if you need settings in addition to Liferay’s default display settings? You could develop a theme or hook with the display options you need, but it’d be nice if you could apply particular display options to specific portlet instances without having to redeploy any plugins. Ideally, you should be able to provide authorized portal users the ability to apply custom display settings to portlets. This saves you from having to change portlet configuration code every time you need new settings.
Be of good cheer! That’s precisely what Application Display Templates (ADTs) provide–the ability to add custom display settings to your portlets from the portal. This isn’t actually a new concept in Liferay. In some portlets (e.g., Web Content, Media Gallery, and Dynamic Data Lists), you can already add as many display options (or templates) as you want. Now you can add them to your custom portlets, too.