Offering a proper resignation may help preserve your rights and benefits.
Why You Should Resign (and not Just Quit)
It's easy to quit your job.
Really, it is. All you have to do is not go to work for a few consecutive days when you should be there, and not let your employer know where you are. After a certain number of working days without communication from you - usually three - your employer is legally entitled to consider that you have quit. That's all there is to it. (Remember the movie "Erin Brokovitch"? The heroine nearly ran afoul of this; she came back to find her desk being cleared out because she'd been out of touch for several days chasing after the polluter story.)
But as you already know life is not that easy. By departing in this fashion you relinquish any rights that aren't guaranteed to you by law. You may not get the salary for the days that you've been absent. You will lose any benefits - medical, insurance, savings plans, etc. - that are dependent on your leaving in accordance with your employment agreement, be it a union contract or the forms that you customarily sign when you start a job. You may forfeit holiday pay and accumulated sick days entitlements. You can count on it that anything you might be entitled to on leaving your job will be handed over as grudgingly as possible and will be the exact minimum that the law states that you must get.
This isn't all. Personnel and human resources types, and employers generally, talk to each other. They have associations which meet for professional reasons and where chatting over drinks occurs after the meetings. You can count on it that the word will get around about the way you've acted; that will do you no good at all. You might get away with it a couple of times but you will quickly find that you won't even get on the short list for jobs that you are well-qualified for. And while you may be able to demand the reasons for which you weren't considered, you're just digging yourself deeper in: you're proving yourself a troublemaker as well as an unreliable employee. You do not need to acquire such a reputation!
Our point is that there is a right way and a wrong way to leave a job. Reasons will occur to you for using the "wrong" way - just simply vanishing from a time and place - but the consequences probably aren't worth it to you. Submitting a resignation letter is the right way to leave your job gracefully.