Role of VFX and Croma in Cinema

Such video are getting viral, which reveals scenes about the shooting. In that video it is clearly seen that the shooting in going on in a closed room, whereas in the film, sky and battle field is seen. The biggest example of such videos are India's most popular movie of 2015 'Bahubali', scene of Bull fight with Rana Daggubati, in the shooting video it is clearly seen that it was not a bull but it was the hero Prabhas. Means how, the people gave a man face to a giant bull face, this is told during the film is made, on this question, some words are told to us like VFX or Croma. https://youtu.be/bU0pxYwAI80 But here we know what does VFX or croma does. Like during watching any film, some scenes make you astonish, that how he must have did this, but the reality can be anything, it's all about VFX and Croma. The most important thing is? Have this made any profit to cinema or by this they have stuffed fake thing in the film.