With the sort bar you can change the order of the dimensions and measures. It is possible to hide the sort bar for different visualizations types. Instead of remarking all your dimensions and measures the sort bar allows you to rearrange them with a smooth built in drag and drop functionality.
Note! From QS February 2018 it's possible to change column order in a table by dragging in the column header so typically a straight table does not need the Sort Bar.
Hide or show the sort bar with just a simple click, go to Visualizations settings --> Choose type of table --> Hide sort sort bar. Want to have your sort bar hidden but still have the option to rearrange your dimensions and measures? Don't worry, just right-clicking the menu allows you to make changes even with fields/sortbar hidden.