+1 to Yooper. Given that you mustn't rack before the ferment is finished, and you can't know if the ferment is finished without using your hydrometer, it follows that you shouldn't take the sample at racking; you should measure gravity before racking, as gravity, not time, is what tells you when it's time to rack.
Now, more pertinent to your question, not only is it unwise from a sanitation standpoint to return samples to the fermenter, you should be drinking the samples. Not to save beer (though that's true), but to become a better brewer. Good brewers know what beer tastes like at all stages of the process, because they've tasted beer at all stages of the process. That helps the brewer detect possible problems, helps him decide if everything is going according to plan.
Yes, young beer can be perfectly foul. But if you know that perfectly foul three-day-old beer will end up as perfectly divine beer at three months old, it's a good reference point for your notes.
You dig?
Bob