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: 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.