Firstly, despite appearances this option does not create new styles - it
records the style + direct formatting that has been used in the document.
I don't think it is at all useful in normal use. I have however found it
invaluable when 'cleaning up' and importing documents containing direct
formatting to conform with styles. You can see at a glance what direct
formatting has been used, and you can select all instances of particular
patterns and apply a suitable style instead.