In the writing test, you need to write by hand, so your handwriting is important.
Here are two words that help to explain why:
1) legible (adj.) = easy to read
2) decipher (v) = work out what something says or means
It is very important that your handwriting is legible. If the examiner can’t read it easily then they will have to guess at the words you have tried to write. The examiner should not have to try to guess whether you have written ‘are’ or ‘one’, for example, or whether or not you have made a spelling mistake because some of your letters look the same (e.g. ‘s’ and ‘r’).
This doesn’t just affect the writing tasks. In the reading and listening tests, you MUST always use the correct spelling. So the people marking the test need to be able to easily decipher the individual letters you have written.
Think about True/False/Not Given answers, does your T sometimes look like F? How will the examiner know which one you have written?
To try to illustrate this, below I have attached two images showing 1) a sample of some handwriting (together with a typed version of it) and 2) an explanation of the problems.
The main message here is that handwriting matters, so practise often.