If I complete a task sooner than anticipated, my calendar should reflect an open space in the recently-completed task's space.
Right now, if I complete a task early or out of order from how I thought my day would flow, the calendar event for the task stays in place and I have to reschedule the task to match what occurred. This isn't ideal because I don't have a true view into how much free time I have in my day and if I might be able to fit more/fewer things in. I spend more time scheduling/rescheduling than I do setting up my day, and it takes me out of flow.
One option might be to convert the task to an all-day task instead of a specifically-scheduled task.