Option to show total value of value that is counted for in pie chart. Sum of all pie parts. Especially valuable in case of a Pane split and you have multiple pies.
OK, so you have a Pie view with the "v" drop-down set to a particular numeric field X, and the "Split" drop-down set to field Y. Let's say X adds up to 53. Do you not see (e.g.) "total: 53" in the toolbar?
Sometimes total is shown in toolbar, but not always. It is not shown when Value is set to Number of records. But the toolbar is often hidden, so in case the total is shown there, users wont see it.
But the Total Value has it's main purpose in case of multiple pie charts created by the pane split (horizontal or vertical). You want a total per pie and not the total of all pies.