One important thing missing is the ability to specify approximate numbers, just like we do in real life.

Let’s say this item is going to cost me $90-120. I’d like to write down just that. Also I’d like to say that there is a 80% probability that I will be able to purchase the item for $90, 10% probability of spending $100, etc.

Then you can calculate all those estimations and probabilities and deliver a figure that is much more useful than just a =SUM() from an Excel table.

(I have used this method of estimation in software dev project management)