I think you should write point to the point and do not add extra materials( which are not concerning the question) for the sake of length. But length do matter. What I think personally is that 4 or 5 pages will be enough for 10 marks question. You should watch marks of the question and then decide how long you should write. So,both are important Quality and Quantity.

I hope I solved your problem.

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Marwatone.