Pronouns help with overall coherence and cohesion in IELTS writing.
Having a cohesive and coherent essay is very important for your overall Band score In both writing tasks in IELTS, especially writing task 2. You should always make your writing as easy as possible for the reader to follow and it should be easy to understand. In the IELTS exam, the reader will be the examiner.
One way to improve your cohesion is to use pronouns to reduce repetition, this is mentioned in the marking criteria for writing under ‘Referencing’.