Actions and action lists were introduced in version 4, and I have used them largely in VCL projects. Actions are a great yet simple way to properly divide application code from the presentation layer, providing an abstraction of something that can be executed and an easy way to bind the execution trigger to one or more UI elements.
The fact that abstraction is available for manipulation at design time is a great benefit in terms of the RAD approach. But at the same time, it keeps your code cleaner than having it spread out through event handlers of your UI elements.
Additional features include the ability to define a hint text and an image of the action (helping to achieve a visual continuity throughout your UI) and to define when the action is enabled and/or visible in a single code point (the OnUpdate event handler).
If you are an experienced Delphi developer, you will be happy to know that actions have been refactored in order to be shared...
