It all depends. What is more important is the reason why you want to compete in the exam. If you know the reason, then you will be motivated enough to prepare. Assuming that you don't really know why you have to prepare for JEE since you asked this question, I will tell you some pros and cons of preparing for the exam. 
PROS

1. The preparation for JEE brings discipline in your life. You can feel yourself becoming more mature with time. It is a very healthy change. And if you are really disciplined, you realise your true potential and the benefits of leading a systematic and organised live
2. It teaches you time management. Nobody would suggest you to mug up every second of the preparation period. Manage your time according to your priorities. The preparation, no doubt, requires a minimum amount of effort which you will have to put in constantly if you really want to achieve it.
3. It teaches you the value of the three most important things in life : Passion, Optimistic Approach and Constant Effort. These three are the basic pillars of success.

CONs

1. You will sometimes feel you are missing out on a lot of things your friends must be indulging into.
2. It is very taxing to continuously put in effort for returns you expect after a very long time. Short term benefits always catch the eye. You have to turn a blind eye towards distraction, which, unfortunately are too many.

There are not a lot of cons if you see it in a positive and healthy way. This is what I learned from my preparation.
It is up to you to decide if you really want it or not.

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