Depending on what this Service Definition is for, you may or may not want to force those new site requests to be approved. You can decide approval settings per Service Definition.
Imposing an Approval Process
To impose an approval process, navigate to the Approval tab in the Service Definition:
To set a process, first slide the switch to Yes:
You can then select an approval template to impose upon new site requests for this Service:
Remember to Save your changes.