3186173 - What is the difference between a To-Do task and an Approval task and its purposes in a Savings Form in a Sourcing Project?

I am working on a Sourcing Project, but I don't know the difference between a To-Do task and an Approval task or its objectives in the Savings Form.

task types, task comparison, task status, form status, sourcing project tasks, task completion, approval process, to-do vs approval, savings form status, form publishing, task owner, approver role , KBA , BNS-ARI-SS-PRO , Sourcing Project , BNS-ARI-SIPM , Supplier Information & Performance Management , Problem