50% weight age is for your scores GRE/ GMAT/ SAT /ACT /TOEFL /IELTS, whichever applies to you, your grades/ GPA, the other 50% is on your profile. What you bring as a student to the university. How well you can contribute to the university. Also how well will you use the university recourses? And this they will be able to gauge from your essay (where you write about yourself) and your recommendations (where a professor/professional writes about you) . So the university gets 2 perspectives to your profile! One cannot stress enough on the importance of these 2 documents. They can save you if you have had a particular low score in a subject and you are genuinely able to explain the reason for it in your essay and show how you have improved. A teacher could also write about your progress in a recommendation.
Essays are of an utmost importance for overseas admissions. But essays rarely stand out! The purpose of studying the course has to be extremely clear. An essay that has a blazing idea/ a research idea, which infuriates the admission committee, is looked upon amiably. Even a obstacle that the student has been working on and how he/ she plans to find solutions through the programme of study is a great point to have in an essay. It has to be genuine and personal.
A single Letter of recommendation can change the perspective of the whole application! That’s how important a Letter of recommendation is! The admission committee gets to review your application through a 3rd person intersection. It is recommended to waive your right to review the letters. A letter of recommendation should be an genuine evaluation and not only recognitions. Focus on the projects that have not got a mention in the application, elsewhere. Choose your recommender thoughtfully. Having a senior position person recommend you is great! But if you have not worked or studied under him it will not carry weightage. Rather a teacher, who has known you over a couple of years and with whom you have worked and progressed, will have more weightage!