You might not use some service codes very often, but you want to keep them just in case. All service codes in SimplePractice are set to active by default. You can easily set service codes as inactive by clicking on the service code in the Services settings tab in the Billing settings section. Just deselect the checkbox labeled Active and click Save.
To view Inactive Services just scroll down to the bottom on the service page and click on Show inactive services. This will open the list of inactive services.
To make a code active again, just follow the steps above to make a code inactive, but just select the checkbox labeled Active and click Save.