This shortcut will insert rows as long as at least one rows is selected. In a table, this shortcut will insert a row above the active selection when only one cell is selected. If you use the shortcut without a row selected, you'll see the the Insert Cells dialog box displayed.
Note: In Mac 2016, this shortcut was changed to Control Shift + (same as Windows), and now control + I changes text to italic. In previous Mac Excel versions, Control + I inserts a row (when a row is selected) or brings up the Insert Cells dialog when the selection does not include an entire row.