Have you heard the different renditions of the "shenbagame" song from Enga ooru paatukaaran? One is a happy version by Mano and Sunandha. The other one is a sad version by Asha Bhonsle. Both versions are basically the same tune and with the same tempo, but you can experience different emotions by the way the singers render the song. First listen to the duet, which is the happy version. Now look at the way Asha renders the song for the sad version. The singer has to basically get into the mood of the song to get the right emotion. This song taught me the importance of bhavam.
Someone observed that Ilaiyaraaja uses the same tempo for both happy and sad versions of a song. For eg) Povoma Oorgolam, Vaa Vaa Anbe Poojai Undu, Vellai pura ondru yenguthu, etc., while many other music directors reduce the tempo for the sad versions. For eg) Poraale ponnuthaiyee, Nila Kaaigirathu (this one is an excellent song), etc. Ilaiyaraaja uses the same tempo and almost the same beats and yet achieves the required emotions. The singer has a major role in such songs. BTW, even IR has uses slow tempo for sad versions such as "Kuyil paatu o vandhadhenna ila maane".
Coming back to the shenbagame song, it is an excellent soothing melody. I especially like the prelude very much. I read that it is based on the scale of sindhubhairavi raag, which seems to be one of IR's favorites. Enjoy the song !