The site admin account is also known as a principal's account. It allows for the management of a single site. Logging in as teachers, assigning assessments as needed, viewing results, etc.
Click on the Site Admin tab and select Users.

Log in, View or Manage a Teacher's Account

It also allows access to running reports via the LGL Data Portal for a single site.
Click on the Reporting Tab and select DataPortal.

What reports are offered in the Data Portal for Teachers and Principals?
See pdf "PrincipalAccountBasics" below and "TIPS_Principal-Access-to-Data-Portal" & "Tips_Principal-Home-tab" at bottom in Attachments section.