Here’s one example that seems to work pretty well. The checked-off items all seem to drop to the bottom too, an added bonus as it helps keeps things visually organized!
Having something denoting that an item is checked is very useful for me. During the GTD weekly review, one needs to confirm if everything marked in the calendar is completed during the past week. With this feature, one can easily tell by viewing the calendar if something has been completed or not, then one does not need to locate to the Dynalist item that has the calendar event.