With Smart Templates version 1.4 and later you can setup the macro to load the contents asynchronously
This is done by checking the option in Smart Templates macro like in the screenshot below
In this case, the page renders quickly and the loading message like below is shown
And the actual contents is loaded asynchronously for you and when it is ready you will see the on this placeholder
This feature helps you to render your slow contents in a more responsive ways, and when you have multiple smart templates using this method you can load the page in parallel (and not sequentially, when using the standard page rendering method)
See it in action below (this happens very quick here)
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