Candidates have to retake IELTS at times if they could not achieve their intended band score due to various reasons, for which they have to prepare for IELTS exam again and boost their score by improving their skills further towards the level of their required score band. This is due to the fact that some universities expect very high band score from the candidates as they provide admission only for the candidates who are having high potential. And for some courses too, the universities seek high band score of even more than band 8 in all modules. For all these categories, it is highly recommended that the candidates have to ensure their English language proficiency before sitting for IELTS else they have to retake the IELTS once again.
Candidates are eligible to retake IELTS as many times as they can to achieve their desired band score but the fact is they will spending ample amount of time and huge amount of money and after three or four times, they lose their confidence, so to avoid all these, Prestige institute recommended the candidates to attend all their mock tests before applying for the IELTS exam. Furthermore, for permanent residency, it mandatory for the candidates to score more than band 7 in all modules which they might fail and consequently can retake the IELTS for one module alone as IELTS does not provide that option to the candidates, so they might be sure that also concentrate on other modules also equally for the consequent exams.
References
https://www.manhattanreview.com/ielts-retaking/
http://www.knowledgeicon.com/ielts/ielts_retaking.php
https://www.canadavisa.com/canada-immigration-discussion-board/threads/…
https://www.ieltsbuddy.com/retake-ielts-or-remark-comments.html