Why do you think people switch jobs from their core field to some other field?Is it good or bad?

With high competetion for scared jobs especially in my country, the need to be versatiled when it comes to finding jobs. It is good in that it helps to keep you in the job market.

Mostly after a person works in any particular field of his/her initial choice, they come to realize that they are having a better & hidden skill in a different discipline which initiates them to take this step.

Yes, it is indeed good for the individual and the company 'cos more your zeal & content of job = more productivity.

It is a good thing. Some times peoples realized that they are having a good experience/ ability which can be utilized in other field also by which they develop them self in a better way. this is useful to the industry also.