Single Activity Upload can only upload one spreadsheet per activity per building at a time. There can be multiple activity types in the spreadsheet, but only one activity. While the Multi - Activity Upload can upload multiple activities of the same categories to numerous buildings.
For example for Single Activity Upload is most commonly used by a user who has a spreadsheet for a particular activity where it is more time consuming to input the data one at a time manually such as an electricity meter supplier statement for 12 months.
While the Multi-Activity excel upload is most commonly used when the user wants to upload a excel spreadsheet or csv file that contains say electricity meter data for multiple activities of the same category in over 55 buildings.