Assuming it worked as advertised (see electromagnetic's comment for thoughts to the contrary), what use wouldn't there be for a way to track people, especially one as unobtrusive as this? Not useful for the average person, but for any covert study of someone it could be handy.
The hope is that if it became good enough, it could be used for forensic evidence. For instance if hair is discovered at a murder scene, you could get evidence about where the murderer likely lives.
That seems like a bolt-on statement to me, included to suggest some possibility of future funding/social good in order to justify a grant or other government funding being used to finance this research.
Scientifically, it's fair enough - hair testing can be used to detect drug use, for example. But people generally drink many different kinds of liquid per day, and only the most consistent and unusual intake patterns would be much actual use. Great for CSI-style plots like 'it's said he will only drink wine made in the village where he grew up...start staking out high-end barbershops.' If you're trying to match a hair found at a crime scene to a particular suspect, you just compare his DNA with that at the root of the hair sample.