You will only be granted exemption if the university is sufficiently convinced that you are proficient in the modules that you are seeking exemption.
If you have done poorly in your previous study, or if you have taken a long break after graduating from your previous course, it might be advisable for you to do the full works. Learning at the university level is progressive - if you miss any crucial fundamentals, you may find yourself struggling through the rest of your course.
Accreditation board may sometimes require you to study a minimum number of years in the specific area before you gain accreditation. For example the Singapore Board of Architects require one to have studied for 5 years in the area of Architecture before gaining license to practise as an Architect in Singapore. If you had sought exemption and graduated in less than 5 years, your degree may become useless in Singapore.