Depends. I can leave my Pu-Erh in overnight, and the flavour is still fine. (But Pu-Erh is well known for that.)
If you're drinking the tea without milk, I can see preferring something weak.
There are some Sri Lankans who do that due to the British influence and I imagine in India as well, but that's not the case with most of the tea cultures.
Also, if you're doing this for health reasons, I strongly recommend avoiding milk and switching to green tea instead: http://www.npr.org/blogs/thesalt/2012/09/27/161895873/health...
> There are some Sri Lankans who do that due to the British influence and I imagine in India as well, but that's not the case with most of the tea cultures.
I wonder where the Mongolians got their milk-tea from. Probably not from the British.
http://en.wikipedia.org/wiki/Suutei_tsai
An old tradition among many Mongols was to not drink water straight. This could have been a result of the Mongols’ belief that water was sacred. It could also have come from the need to conserve water
I'm willing to bet she was doing it for some sort of DIY health thing. People do silly things like over-doing something if they think it's good for you. Well, that then makes it bad for you.
There's a great book on all this called The Book of Tea by Okakura Kakuzo :
http://en.wikipedia.org/wiki/The_Book_of_Tea
A very good read on the subject. I think Google Books probably has a free translation.