There are millions of blogs out there. Literally. But there should always be more. It might be seen as filling the Internet with junk, and but I think everyone should have a blog.
It doesn't matter what you blog about, or whether anyone will read it. Blog for yourself if you need to, but you should blog. The why is simple, it will help you arrange your thoughts in a concise manner and improve your communication skills.
It's always been a required skill of business to be able to communicate, but they key is to do it well. How well you communicate is usually subjective from whoever it is you are communicating with, but everyone can improve in this area.
Personally, I tend to blog about tech and development. It's my career, I'm involved in it regularly, and it helps me stay fairly current. I also have blog posts where I've solved problems I've had, but have created a post because I'm going to have the same issue again in future. I blog for myself.
Sure, at some point someone might look at it when I apply for jobs. But the knowledge I've managed to impart on these pages might just help get me the job. It might prove my communication skills. Or it might sink my application completely. It's always a risk, but I believe I am a better communicator as a result of blogging.
Get a blog out there and blog about anything. A career, a hobby, something you are passionate about. I would advise to stay away from controversial opinions as a hobbyist blog, as this will likely come back to haunt you; but just blog.
It doesn't have to cost anything (other than time), as there are loads of free blogging platforms out there. If you ar new, stick to a free one and learn about blogging first. Wordpress is the industry leader in this space, and requires zero technical knowledge to get running. If you are happy to pay someone to host your blog, then check out Ghost (this blog runs on Ghost, and I switched from Wordpress).
Don't like those options - then hunt for another one. Better still, try a few out and collect your thoughts. There's a blog post to be made about that!