Viva-voce is an essential and integral part of any professional curriculum. Its supposed to be just as scary as a theory examination and sometimes even more as its an oral examination. Though I had given viva voce at school level I don’t remember anything about it. You can read Ishmeet’s experience of a school viva here. In a field like Engineering or Medical, practical knowledge is much more important than theory. Viva-voce tests just that.
I don’t know about all but in many private engineering colleges viva-voce serves as a source of entertainment and frustration for the external and the internal examiners respectively rather than an ordeal for the students . The increasing disregard in students for studying before practical exams and the decreasing sincerity and quality of students in engineering can be attributed to cropping up of engineering colleges like mushrooms and the trend of not failing anyone in viva in private engineering colleges.