There are 3 types of data that can be exported from the SMS: Achievement Data, Student Archives and Enrolment Statistics. These exports are available to clerical and admin users in the SMS.
After you click the 'refresh' button, a new file is generated and will be available soon (depending on the size of the file). The file is then available and will not be updated until the 'refresh' button is selected again.
To avoid office staff from having to click in order to generate large amounts of data "all at once," these exports have been created. Given that each export takes significant processing, server performance can be impacted (making users unhappy). Therefore, these features wait for "low-server load times" to do the generating.