The ultimate users of the cell store are interacting with it through a UI that looks like a spreadsheet.
The cell store API provides endpoints for creating spreadsheet renderings on the fly.
A spreadsheets provides a two-dimensional, user-friendly view of a component by slicing and dicing dimensions.
UIs can be built on top of the REST API to provide viewing (with GET requests) and editing (with POST requests) features on top of these spreadsheets. For example, clicking on a fact allows viewing its aspects, or editing its value, and dragging-and-dropping headers rearranges the slicing and dicing structure.
Spreadsheets correspond what the user actually sees, i.e., the spreadsheet interface itself.