It is something that not everyone really thinks about deeply.
For new graduates, please refer to the Contract of Service laws drawn by the Ministry of Manpower. These laws or terms could be very useful to you especially in this era where moving from one job to another is a common practice.
Not understanding the terms of contracts or lack of it could land you into trouble or even get you shortchanged. For example, for new graduates, it is ok for you to sign for a job but cancel your intention in the case you decided to go for another. This is permitted according to the Employment Contract law. Of course this is for situations where you only signed to accept the job offer and have not yet started. Those who already commenced on their jobs would have to carefully look at your terms of service to know when you can actually send in your letter of resignation for example.
Knowing these laws could also save you from being shortchanged in the case that the employer refuses to release you citing the employment contract as your obligation.