One of the most important skills to learn in Excel is understanding how to reference values and arrays. Whatever you use Excel for, you need to know how to specify the location of a value or array. One could argue that it is the most important skill.
This does not just apply to formulas, but charts, PivotTables, formatting, validation rules, etc. It all boils down to being able to tell Excel the locations of the values or array that you need.
Data could be stored on the grid, in a table, a defined name, a spill range, an array ...
