The command Repeat 
in the Quick access toolbar repeats the last command that you used with exactly the same settings.
This is especially useful when applying formatting. If, for example, you have assigned a different font to a cell via the ribbon tab Home | group Character, you can then navigate to other cells and simply use the command Repeat 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 in this manner as often as desired.