Never let your audience guess what you are trying to say, your writing should literally speak for itself. When your content has too many errors, it becomes difficult to read and understand. Although, one or two errors can be skipped by readers, but glaring grammatical errors can minimize the impact of your content. Also, it can make your writing difficult to read and digest.
Quality readable content is key here. Google, for example, will recognize that people are leaving your site soon after arriving if they perceive that your site or blog is full of junk content. This is called "bounce rate." If your bounce rate is high, then people are quickly leaving your site. But for the sake of your business, to build your online reputation and brand, you want people to visit your site, stay for a while, and then keep revisiting over the long term.