It is a common sight that students (in some cases, teachers, too) worry about the ‘complex structures’ aspect of grammar score in their writing tests. It is nothing but a waste of time.
It makes no sense when students have several complex structures (joining clauses in one sentence using linkers) with full of errors. In the IELTS test, error-free sentences are of great importance if someone wants to achieve an 8-band score. Let us look at the marking parameters here:
Band 8: most sentences are error-free
Band 7: frequent error-free sentences
I explain this fact to students, and yet, they fall in the trap. I can see that most students can write sentences with more than one clause using linkers, such as while, where, when, because, yet and as among others. They are perfectly be categorized as complex structures and do connect ideas. So, why do we need to press the need for more complex structures? I guess we do not need more than that.
Test takers must concentrate on error-free sentences, and should focus on this aspect carefully rather than being experimental on something on which they may mess up their write-up. And, if someone is not able to produce such error-free sentences, they should rely on simple sentences. In the end, your grammar mistakes count!