Quick, clean, and to the point

Drag and insert copy

Windows shortcut 
Mac shortcut 

By default, drag and drop "cuts" cells like Edit > Cut, and overwrites values at the new location. Use this shortcut to copy values and to insert cells at the new location. This also works when dragging entire rows or columns. This is a good way to duplicate a row in an Excel Table, since Tables do not allow you to copy and insert paste entire rows.

Just want to thank you for these snippets, this is just so awesome and has certainly increased my ability to use Excel more effectively. -Peter
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