If using Google Sheets, you are giving Google a lot of information about you. Google can and will read all of the contents of every file you upload and use the information for advertisement targeting.
As a software developer, I'd say the majority of the processing power needed at the server side is the advertisement targeting information collection. The software itself, if you could use it without ad targeting, would require relatively little resources.
The storage part also needs some resources, but that depends on how much storage space you need. You can calculate it by figuring out the energy usage of various storage technologies.