A blog can be a razor blade or a butter knife.
It depends on what your goals are.
I use blogs as top of the funnel lead generation devices.
For example, you may have a website selling shoes. You can’t really get away with writing blog posts only about different shoes in your inventory.
Instead, you’ll write about what it means when your shoes hurt your feet, how to wear teniss shoes with suits, when to wear cap toed shoes vs wingtips, when leather boots are appropriate, etc etc.
People searching for those terms will land on your site, consume the content, click around, maybe subscribe and buy something.
You can also use it directly for affiliate marketing by writing reviews and such.
Again, blogs are mainly for top of funnel and sometimes middle of the funnel. Use them to cast a very wide net. They don’t work as well for bottom of the funnel.