Sometimes the name of the column is not enough when labeling bar charts. Also for data tables with a lot of rows, it is very inefficient to create columns just because of the lack of custom labeling. It would be nice if one could add labels with custom expressions.
It´s already possible to change the axis labels by including a new name in the expression. E.g. to Display "Total Sales" instead of Sum([Sales]) on an axis you could change the expression to "Sum([Sales]) As [Total Sales]". Is that what you are looking for?