First of all the greatest advantage that the airport has had right from the beginning was the availability of large tracts of land around it for expansion(At least till the turn of the century). First came the Meenambakam terminal that still continues to be part of the Cargo terminal at the airport. Then came the Kamaraj terminal and Anna Int'l terminal next to one another. This model was best suited for linear expansion for both domestic and international terminals. As int'l traffic increased Anna terminal was expanded further down to add three more aerobridges. The domestic apron was expanded to accommodate more narrow bodies without the requirement for expansion of the terminal itself. Both terminals were built for good capacity.
The highlight was better utilisation of available space. Chennai airport always experienced a steady growth or drop in traffic and never a drastic fluctuation. Innovative ideas which were never experimented at Mumbai or Delhi were used here. Traditional space plans were done away with and models that suited the needs of the situation were implemented. Also Chennai airport was the first to implement cross runway operations along with mumbai. Walkalators which were conceived for the new terminal at Delhi have been commissioned at Chennai airport at concourse level.
The concept of integrated terminal seems to have caught the fancy of everybody. All major airports that have been modernised or under modernisation are following this for better utilisation of space at air side as well as terminal side. Chennai airport on the other hand is going for separate expansion of domestic and international terminals. But it hasn't failed to understand the benefits of the other model. So the concourse level of both terminals of the airport have been connected with travelators for easy transit. This means domestic aircrafts can park at international terminal when it is empty but the passengers can reach the domestic terminal easily and vice-versa. This combines the advantages of both the terminal models.
Finally, Chennai airport has always undergone modular expansion and continues to do so linearly. This eliminates the need for sudden or drastic change in airport operations. It would be better if the air side was also expanded similarly like rapid exit taxiways etc.