Generally the standard of writing of most students in exams deteriorates. Bit of a gross generalisation, but a lot of the kids that do better have 'bad' handwriting, as a lot of them tend to try to fit as many words as they can into X number of minutes. So long as your handwriting is legible, you don't lose any marks for bad handwriting. Technically even if your handwriting is illegible, you don't technically lose any marks for it either - however you would lose marks for fluency if the marker has to ad lib every fourth word or so.