Application.CutCopyMode=False is seen in macro recorder-generated code when you do a copy/cut cells and paste . The macro recorder does the copy/cut and paste in separate statements and uses the clipboard as an intermediate buffer. I think Application.CutCopyMode = False clears the clipboard. Without that line you will get the warning 'There is a large amount of information on the Clipboard....' when you close the workbook with a large amount of data on the clipboard.
With optimised VBA code you can usually do the copy/cut and paste operations in one statement, so the clipboard isn't used and Application.CutCopyMode = False isn't needed and you won't get the warning.
For optimising macro recorder-generated code you can merge adjacent Select and Selection statements and refer directly to sheets and ranges.
Macro recorder code: