Imagine that an answer gives three correct points and five incorrect ones. Assuming that the student believed everything they wrote, the value of correct parts is reduced by the others. So, don't assume that writing drivel will help you because the professor might find some random value in it. As I grade, I also get an impression of the care with which the answer was given. Spelling and grammar do count.
Grammatical errors can change the meaning of the sentence.
If you're killed, you've lost a very important part of your life. All of these can lower your grade. If the test really was long, a general factor can be added to the class results. However, more frequently, many students finish the test but others do not. Generally, this reflects differences in the quality and quantity of studying.