Users that are just starting with the energy dashboard often go through a lot of trial and error getting the correct entities added. Or they get mixed up and their history ends up being wrong and having several miscalculated energy readings.
Although there is the adjust sum statistics options, sometimes users might want to simply start all over. But to do that they would need to either delete their whole database or manually go in and delete tables (not something an average user would have experience with). A simple Delete All Energy Statistics button would be useful in such situations.