I have been receiving a lot of "Should I quit my job to improve my chances of getting into IIMs and cracking CAT and other exams?"

Know what to do; do what you know.
If you are good at something, it doesn't mean you have to make a career out of it.
If you are good at something, it doesn't mean that you have to charge for it. Just because a fictional character said so doesn't mean you have to formulate your entire life around that. 

But if you are really clear about your goals and motives and have decided to really pursue your passion of becoming an MBA Wala, you need to analyze just how much your job is costing you.

First of all, is your job in the same field that you want to pursue?
Secondly, do you really think that quitting your job can help?

You also need to factor in the uncertainty. No one can be sure of the outcome of the actual exam. It is a possibility that you might get into an accident, get sick, or get stuck somewhere, disabling you from even writing the exam in the first place.
Know the risks, the uncertainty. Know that literally anything is possible.

Now, analyze everything; see where it takes you. Now, read the last line carefully:
"Literally anything is possible."
ANYTHING.

That involves your being a 100 percentiler, getting into IIMs, or even Harvard, if you are that ambitious. If you really think that your job isn't taking you anywhere, that it is disoriented, detached, and disintegrated from your actual goals; that your time is better utilized elsewhere; that you cannot learn or grow professionally in the organization; and that a change of jobs isn't really feasible, then by all means, you should quit your job.

But if you do decide to quit your job, make sure to make a decision that you will not regret, regardless of the exam's outcome.
Make decisions with proper thoughts; do not waste your time in regrets. 

Be confident in your decision and study with every fraction of your body.

Thanks & Keep Working Hard.