Many forms in the SMS have a checkbox labeled Mark Complete at the bottom. This box exists to allow users to start a form and then return and edit it later - rather then needing to keep getting a notification message that the form is incomplete. It also serves to tell the system that the form is expected to be completed and that any internal processing that may use stats from the form can commence.

Do not confuse marking a form complete with signing (authorizing) the form.

Mark Complete tells the system that you are finished editing the form. Once you mark a form complete it is locked and cannot be edited (except by an administrator) unless it is either re-opened (which is only possible if it hasnt yet been signed) or rejected.

Authorization is a formal digital signature that initiates the workflow processing and is recorded in the audit trail. Authorizing the form sends it along to the next person in the workflow.

An analogy might be:

Mark Complete is like hitting Print on your computer.
Authorizing is like signing the printed form and faxing it to someone else.