It is necessary to have some hobbies.To,
1)Clear your mind:-Focusing  on a hobby help to clear your mental palate.
2)Ignite your creativity:-When the mind focus on something it enjoys.So if we have a hobby our mind will enjoy.
3)Explore new social oppertunities:-Hobbies encourage you to interact with other people.
5)Find stress relief
6)Concentrate on unitasking
7)Boost your confidence

It is necessary to have a hobby because in this modernised world , Recreation plays a very important role.It gives us a relief from all tensions and problems.
Hope it helps and pls mark as the best answer. :-)
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