What is the purpose of IELTS, in relation to other Cambridge exams?

Compared to other Cambridge exams, the IELTS is much more useful for immigration purposes or for university admission. Other Cambridge exams such as PET, FCE, and BULATS are used almost exclusively for employment in private companies, instead of being used for the formal granting of medical licenses, the issuance of visas of qualified migrants and acceptance in the degree programs.