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The fact that input from a panel can be notified not by completion of the &PANEL statement but instead by the arrival of a trigger message on the procedure's internal request queue means that a procedure has the ability to wait for more than one source of input to act as a trigger for it to resume processing.
For example, consider a procedure that has the role of maintaining a dynamically updated screen display which has to be refreshed with new information as soon as it arrives, but which can receive an input command from the screen.
Such a procedure needs to be able to listen for new information that is to be displayed as well as listening for input received from the screen display.
By designing the procedure so that it receives all its input via &INTREAD TYPE=ANY, it can receive new display messages from its dependent response queue (for example from other procedures operating in its dependent environment) and notification of screen input via its dependent request queue.
This concept therefore allows a procedure to have a single point in its logic at which it can wait for multiple different forms of input, and so synchronize its processing of different input streams.
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