Google itself says "Don’t rely on Bard’s responses as medical, legal, financial or other professional advice. You are responsible for your use of code, which may be subject to an open-source license."
Currently, Bard suffers a few disadvantages including giving repetitive responses. If you're fluent in English, you would find it more limited in terms of creating different sentence styles. However, if you're a non-native English speaker with not very good command over the language, Bard can help you improve your prose skills initially.
Another disadvantage is that Bard wants to be seen as neutral or not very heavily biased towards extreme viewpoints. Despite its ability to do accents and dialogues, it isn't very comfortable with colloquial and everyday speech.
If you want to use Bard to help you with your writing, the onus is on you to apply your mind and tweak your audience expectations for better quality output. If you're planning to use tools like Bard or ChatGPT to pass an examination or publish books and content, do remember that plagiarism software may detect any malpractice. So it's best to use these tools as a brainstorming software.