If you are applying to an MBA program, you probably need to take the GMAT. Many MBA programs require that you submit a GMAT score for the admissions process. Your GMAT score gives the admissions committee another tool to use to assess your skills and compare you with other applicants.
But if you are seeking a career in business, you are probably resigned to being continually assessed and compared. The GMAT doesn’t attempt to evaluate any particular subject area that you may have studied, but instead it gives admissions officers a reliable idea of how you will likely perform in the classes that make up a graduate business curriculum.
Although the GMAT doesn't rate your experience or motivation, it does provide an estimate of your academic preparation for graduate business studies.
Not every MBA applicant has the same undergraduate experience, but most applicants take a standardized test. Other admissions factors, like college grades, work experience, the admissions essay or essays, and a personal interview are important, but the GMAT is an admissions tool that admissions committees can use to directly compare you with other applicants.
The most selective schools primarily admit candidates with solid GMAT scores, and good scores will certainly strengthen your application to any program. Very few students achieve anything near a perfect score on the GMAT. Even if you don't score as high as you want to, you undoubtedly have other strengths in your admissions profile, such as work experience, leadership ability, good college grades, motivation, and people skills.