Freakonomics has a post which claims - "eliminate trays from cafeterias", especially in schools and colleges, and it has been found that people "buy (or take) less food and subsequently eat less and throw away less"!
In this context, even worse than trays are the massive steel plates (intended to carry curries in small steel bowls) used in college hostels (I distinctly remember those massive plates in our hostel at IIT Madras) and in South Indian restaurants for thalis, where the entire plate ultimately ends up being used for mixing curries and eating rice (since the curry bowls invariably tend to get placed outside before eating). The size of the plate itself leads to over-eating and if you throw in the typical South Indian habit of a second-helping, the total quantity consumed becomes much higher than using a normal plate.
So, it leads to the question - Are Saravana Bhavans and their ilk just as culpable of causing obesity as McDonalds? And (going by the aforementioned explanation) since the answer appears to be on the affirmative, it may strike a chord with their health-conscious diners (atleast in cities, and especially those outside South India), for Saravana Bhavan and other South Indian restaurants to move over to smaller plates. This will ensure that their food is not only tasty, but also healthy! The smaller helpings (at the same price) makes for sound economic logic and will naturally improve their bottom-lines, besides keeping waist-lines of consumers trim!
Alternatively, the size of the plate can be maintained by using those plates with fixed/built-in sockets for pouring the curries. This would nudge customers to keep their helpings small without drawing any criticism on reduced portions!
Also see this article in the Times.