In an average Software Development project for a Big organization there could be over 100 tasks in progress (I have had them with over 3000) in 20 or more streams of effort.
Some of these may be ahead of schedule some may be behind and some may be on schedule
In addition some may be below budget some may be over budget and some may be on budget
So if someone asks “Where is the Project at?” how do you give them an answer that makes sense?
That is what Earned Value attempts to do