Sharing and collaborative editing. Being able to coordinate some process via a shared spreadsheet in a browser is efficient and resolves all issues of conflicting versions. Think of an overview of who is going to the office on which days this week (useful in times of working from home due to Corona).

Responsiveness is not the primary concern here: good enough is fine for most purposes.

This is not a replacement for a proper spreadsheet editor (I prefer LibreOffice myself); it's a tool to collaborate on tabular data with a group of people and minimal overhead.