People blog for various reasons. It can be a useful resource to reference back on things for business or personal use. Blogging allows you to create your own portfolio and is a way to establish yourself within the global community. It also can be used as a reflection for your life as a takeaway for your future self.
Having a blog can also be a good way to make money and to gaining an audience.
As you grow your content on a blog, it can lead to other opportunities. Blogging is also a great to see how impactful your words are for your readers.