It makes perfect sense: the "natural" lines would give India two time zones; combining them into one half-hour time zone gives the whole country the same time.
It did cause problems with the early Bell Labs Unix releases, which didn't contemplate that a time zone might not be a whole number of hours away from Greenwich.
Surely India as a large federal nation would be OK with two time zones! It makes about as much sense as China having one time zone for its sixty degrees of longitude.
You don't have to adjust the clocks though, you can adjust business hours instead. Just look at Spain, which shares the same timezone as Poland: they simply wake up/go to bed later on the clock, but not with regard to the sun.
Spain is a good example of a politically-motivated time zone. Prior to Franco putting the country in CET to be in line with Axis powers, it was in GMT, which makes a lot more natural sense.
> they simply wake up/go to bed later on the clock, but not with regard to the sun.
This defeats the purpose of having time zones at all. People generally prefer the sun near overhead at noon; otherwise we would all just set our clocks to UTC no matter where we are. It would certainly make programmers' lives easier ;-)
The offset between local noon and time-zone noon is never that large, nowhere near what it's like in China, and it actually puts the center of the country closer to solar time. So it seems a reasonable thing to do, better than having the TZ line right in the middle where the railroads will keep crossing it.
It did cause problems with the early Bell Labs Unix releases, which didn't contemplate that a time zone might not be a whole number of hours away from Greenwich.