How to activate and app
Step 1) head to the app section:
Step 2) Select activate on the required app:
Step 3) Accept terms and conditions and hit activate:
Step 4) Application should show installed:
Step 5) If still showing as inactive, refresh the page:
How to deactivate an App
Apps cannot be deactivated from within a project once activated, to remove an activated app the entire project would need to be deleted as per the "how to manage projects" article.
That being said, there is no penalty or penalisation of having an app activated.