What's the difference between extending a goal and moving a goal to another goal plan?

When you move a goal to another goal plan, the goal is no longer associated with the source goal plan. For example, you move a goal to another goal plan when you want to associate the goal with a different performance document.

When you extend a goal to another goal plan, the goal is associated with both source and target goal plans. Except for the goal weight, any changes to the goal are visible in both the source and target goal plans after you extend the goal. For example, if you couldn't complete a goal before the end date of the source goal plan, you extend the goal to another goal plan to continue working on the goal for an extended duration.