It is quite common for employers to take up medical insurance benefits for their staff nowadays. However, if you are one such lucky employee please evaluate the following facts :-
Has this coverage been extended to cover your spouse and children as well? (for those who are married)
Is your existing coverage adequate in covering the medical expenses required based on today's standard of living?
Will you be staying on as an employee in your present company for the rest of your life?
If not, do you know that your medical coverage will be terminated the minute you leave your company?
If you have a major claim in the near future, do you know that you may not qualify to apply for another medical policy after that?
If "5" happens, your next employer may not want to take you in because that will incur additional cost to them in terms of health insurance premium.
It is always prudent for employees to have their own personal medical coverage to cater for the transitional periods of between employment.