Recipe kit instructions should be ignored after the part where they say "and then pitch yeast." The best reason I can think of for why they'd tell you to rack before fermentation is complete is to ensure that your beer creates a nice CO2 cushion to keep out air. Then again, any kit that told me to listen to the airlock would be complete BS in my opinion.
The advice that you get from the combined wisdom and experience of 10,000+ HBT members is to rack after fermentation is complete. This is what I do, and this is what just about everyone here does. The advantage to waiting until fermentation is complete is that you end up with a much clearer finished beer. There will still be enough activity in your beer and enough CO2 dissolved throughout your beer to create that cushion of protection.