Duplicate Previous Transform
Copying and pasting can be a big time saver, but not if you need the same object many times at an equal distance. In this situation there is a much bigger shortcut.
When you drag an object while holding the Option Key, not only does it duplicate the object, but Sketch also remembers how you duplicated the object relative to the original object.
Now if you press Command - D, you can repeat your previous duplication over and over again to create evenly spaced duplicates very rapidly