One reason to use an explicite Platform.runLater() could be that you bound a property in the ui to a service (result) property. So if you update the bound service property, you have to do this via runLater():
In UI thread also known as the JavaFX Application thread:
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listView.itemsProperty().bind(myListService.resultProperty());
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in Service implementation (background worker):
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Platform.runLater(() -> result.add("Element " + finalI));
...