This is a pure curiosity question, inspired by questions I have seen here.
In the USA, it is better to stay with a job while searching for another one, and only resign with a definite written agreement on the new job. It maintains continuous income, and employers tend to favor employed applicants. A responsible employee will give a couple of weeks notice, but even that is often not enforceable.
I have seen the same advice given to people in India.
From my reading of discussions here, I see a couple of differences that may matter. Notice periods tend to be a lot longer, and a lot more strongly enforced. The employee needs a relieving letter from the old employer to start the new job, and any delay in getting that can delay the new job start.
Given that, I would expect there to be an advantage to having already quit, and being able to say "I can start working for you next week", rather than "I can start working for you in three months."
In the experience of people who have been involved in job searches in India, as employer or employee, which is better, to currently have a job or to be free to start work immediately?