In big countries, such as India or Russia, which have the area spread over a couple of time zones, it is well advised to use one normalized local time for this particular country.
Why do that? Well, it would be quite a problem if people doing business in their own country but with people from different parts would have to adjust their clocks every time. The same goes for travelling between places. Also, how should we mark the borders of one zone and the other? What if it goes directly throuch a city? How to even measure it well?
Those and many other problems are the cause of using the local time instead of
the geographical one.