The Repeat command 
in the Quick access toolbar repeats the last command you have used with exactly the same settings.
This is very useful especially when applying formatting. If, for example, you have assigned a different font to a cell from the ribbon tab Home | group Character, you can then navigate to other cells and simply use the Repeat command there. These cells are then formatted in the same font – as if you had chosen the last command once again, with the same settings.
There are many other commands that can be repeated as well.