Often results of completed tasks could not be approved right away and approver needs a way to request changes to be applied.
Some popular use cases are:
Preparing multiple revisions of some document.
Preparing specification, quote or invoice.
Negotiating a job offer with candidate.
Preparing copy and illustrations for a new post.
Working on a document translation.
In Metatask you can use Approval task to create a review cycle like on a picture below.
Here's how to configure your process to allow approvers requesting changes:
All tasks which may be redone should be moved to separate group with "one by one" task's order (if you need parallel brunches somewhere inside this part of workflow, you can add another group inside this group and set parallel execution)
The last task in group should be "Approval" with "Approver can request changes" flag is set
So this group will be a cycle, all tasks in this group will be processed multiple times from the first task till the last task (Approval).
Each time when approval becomes assigned, assignee decides should cycle be stopped or work should be redone again. To stop the cycle assignee should grant her approval. Assignees should click "Request changes" to initiate new iteration.
As soon as cycle it stopped, next tasks becomes assigned.