In a Dual degree course, you are allowed to do a Bachelors and a Masters degree in a single course.  A Dual degree lets you complete the two degrees in just 5 years, whereas, individually the courses would entail 6 years.

However, the important thing to note about Dual degrees is that it is more suited for those students who are oriented towards higher studies and research work. Thus, even before joining the course, you might have to take a decision about how you want your future to unfold.

There is no such disadvantage it's depends on your future plan.

Good Luck!!