Thanks for all the explanations on the reasons why someone may suggest
watering the lawn light and frequent.

Although my lawn only has one thin layer of top soil over sandy soil,
I still need to water for a long time (45 to 60 minutes) before the
water can reach down 6" deep. If I only watered 15 minutes (as light
and frequent watering), I would probably only water to 1" deep! Seem
like I am much better off sticking with deep watering (but
infrequently), and should work on improving the soil.

Jay Chan