Update tasks so you can predict your project's end date
There is only one thing that will never change in your project, and that is the fact that everything will change constantly. We cannot count the number of times our students have brought up this fact as an argument for the statement that it has no use to try to plan a project. "We cannot predict the future", is often said.
We totally agree, just like we cannot exactly predict on what minute we will be home when driving back home after a holiday. We do like the GPS in your car however, which takes all assumptions we CAN DO and transforms this into the most likely Estimated Time of Arrival (ETA). And when we hit a traffic jam, it will start adding minutes to this ETA, telling me that I have to change my strategy (average speed for example) to catch up. Because I know this well in advance, I might still have enough buffer to catch up.