The short answer to this question, which I get asked often, is NO! Students sometimes believe that if they write long essays for task 2 then they will be able to pick up more marks. The examiner may not welcome 350 words of text – so as a writing strategy it is foolhardy.
Firstly the examiner is looking for a cohesive whole (cohesion is one of the band descriptors) he/she is looking for something that flows well from beginning to end. Examiners want something that satisfies the question and convinces them of your ideas and gives them evidence as to why you make the points you make. They really want to give you band 7 or 8(I know this because I used to be an examiner) but they can’t if you don’t satisfy the criteria!
The examiners do not have much time to read your task but they are all well trained in looking for what they need to find in order to give you a high band and quantity is NOT a factor. They will look at your grammar, vocabulary and things like complex sentences – but what they really want is clear, concise writing with good points well supported and clear examples. 250 – 280 words is easily enough to give the examiner this and it also stops you from making too many mistakes and gives you time to plan well and check your work too.
Why would you want to create a long piece of work that takes time to complete, doesn’t allow much planning time or checking time and is more likely than not to ramble and go off the point and have lots of errors which you can’t check? Why risk this?
IELTS writing is NOT creative – it is academic, formal and practical. If you want to be creative in your writing find other types of writing to do - but in the exam stick to what you can produce without error in the time you have and make sure you allow enough time to plan well and check at the end. 300+ words in very unlikely to give you this time.
The more you are in active control of your writing the fewer errors you will make and the better the tasks you will produce.
If you crave creativity then write a novel but please don’t try it out in your IELTS Writing exam!