What's the difference between distributing and calculating task assignment period amounts?

By distributing amounts, you ensure that updates to amounts for any period are distributed across all open periods based on the spread curve for the task assignment. Your changes aren't saved or rolled up to the task assignment.

By calculating and saving amounts, you ensure that amounts for each period line are recalculated based on your updates, amounts roll up to the task assignment, and all your changes are saved. If you updated the amounts for particular period lines, amounts won't be redistributed to other periods based on the associated spread curve.