Who can start the workflow
Any user with edit permission for the spreadsheet file can start the workflow.
How many reviewers and approvers can be added to a workflow?
20 reviewers and 20 approvers can be added to a workflow.
What happens once the workflow is started
Once the workflow is started, only the reviewers or approvers (based on whether it is a review or review and approval workflow) will have the permission to work on the file. Everyone else, including the file owner, can only view the file and make comments.
What happens after the workflow is completed
Once the file is reviewed, the owner receives an automated email stating the current state of the file, and the file owner (and the collaborators) will again gain edit permission.