Even this can be broken down by directors such as KB, who exploit songs to their fullest capacities. Generally one to two songs in a movie serve its purpose. Songs in TF are an excuse for the wildest of imaginations. Long before MTV, our guys have done it and in a million ways too. In some other forum, someone commented that an actress breaks into a song, while being violated and said this was illogical.
Songs sometimes are a break of monotony.
I remember in old Sivaji movie and even is some horror movies, songs are used to break the tension that would be building up in the viewer. I could go on and on, but will hold, for others' comments. But I can safely say that songs in TF will not disappear in the near future. I'll write soon. I think it really depends on the story line of the movie.