Hello

First off all these preparatory courses are not all necessary for you take the main reason that  is that you can study anywhere without these expensive courses that market offers like aakash etc.

You have to study , you can study through videos etc but if you are losing focus these institutions may be helpful. And they offer everything at a same place mock papers , test etc but entrances exams are for basically held for scholarships or for dividing you in different classes to prepare.

Entrance exams  are tough that is no doubt as there are many students and less seats .

But hard work pays off isn't it no matter where you study you have to be focused and have confidence. These courses in other way boast your morale nothing else .

So best of luck !!