Question

What does the Export option in the Extraction Rules activity do?

Answer

This Export option saves the layout created in the Extraction Rules to the .fft file.  
The exported .fft file can be opened in the FlexiLayout Studio. This can be done by renaming and substituting the original .fft file in the Templates folder of the FlexiLayout Studio project.
 
Below is an example, where fft_test_old.fft is an original file that was renamed and fft_test.fft is a renamed Extraction_Rules.fft exported from Advanced Designer: