I have had pupils who make lots of silly mistakes, often because they jumped in too quickly without reading question properly. Usually explain that the question setters are sneaky and try to put in some questions to see if you can think that bit harder.
Marking the paper together and pointing out how much they would have got if they hadn't made the silly mistakes ( which they usually spot straight away for themselves) often works. It can be the difference between a pass and fail.
Also marking machine can;t give the benefit of the doubt like a class teacher often can