Your guide would help you throughout your PhD, but do not expect that all practical advice would necessarily come from the guide. As it happened in the case of Venugopal. When he was doing his PhD from VTU, his guide was supportive and supervised efficiently throughout. During the final year, when he was closer to thesis submission and final viva, his guide told him to prepare well for the viva and suggested tips to handle the defence well. However, like how I said before, not all practical advice would come from your guide. He did not mention him about thesis proofreading.
Venugopal was in touch with other scholars from the university and during his regular interactions with them, he understood that it was very important for him to get proofreading done for his thesis. He acted pro-actively upon some wise advice and took external help from experts for thesis proofreading. And to his surprise he discovered that many of the sentences in the thesis were meaning just the opposite of what he wanted to say. This was largely because of English being a second language for him, sometimes he made the wrong choice of words or sequencing of the sentence which completely turned around the meaning of the sentence. Other than that minor spelling and typo errors also altered the meaning of the sentences. Here are some example paragraphs from Venugopal’s proofread thesis:
In the short term, output in the goods market is determined by the level of consumer demand. The demand for goods is itself a result of a number of different factors including the confidence that consumers have in the economy (which says whether they are happy to spend on non-essential goods or would rather save for the rainy days they may perceive to be ahead), as well as fiscal and monetary policy.
The major defining factor that we will consider here is the disposable income. Naturally, the more disposable income a person has, the more they will spend and the more goods they will consume. Economists usually consider that a (positive) linear relationship between disposable income and consumption exists of the form
It came as such a relief to him that the external and internal reviewers did not have any issue with the quality of his work and his thesis got cleared in the first go itself. He thanked that good sense prevailed on time and he took the right decision to go for proofreading. Else, surely the completion of his PhD would have been delayed by a year, at least.
So, to get perfection in your thesis and to ensure your articulation is impeccable, meaning what you want to say, proofreading is a must!