Answer: Out of 50 odd subjects that you study over the 4 years of engineering, 45 are bound to common between these two streams, give or take a few. In Mumbai university, IT and CS streams had 45 out of 48 subjects common. That says it all. The difference is usually in subjects that will not matter unless you choose to do MS/Ph D in one of those subjects later. (Even there, the differential subject is usually an advanced level of a course, the basic level of which both streams would have studied in a common course in one of the previous semesters). That way, even an MS/ Ph D in the differential courses would be applicable to students of both streams
Essence of the Answer: NOTHING.