Cambridge English Qualifications are widely recognised in European countries by employers, and increasingly recognised in Asia and South America. C2 Proficiency, C1 Advanced and B2 First are General English tests, so the preparation courses are great for learners who want to study General English but with the extra focus of preparing for an exam.
The tests are not intended to measure English ability for entry to English-speaking universities and other institutions, but a pass in one of the Cambridge exams is often accepted as evidence of English-language ability for this purpose.