That's what he meant. You shift-click to issue multiple move commands in order to guide your troops around major obstacles if you want to run a different path from the default one that the flow field would generate.
Its not just the default one the flow field would generate. Other pathing methods would generate the same path as the flow field. flow fields are essentialy just a way of getting more than one unit to uee that same path so it doesnt have to be worked out 300 times per click.