There is the benefit of ranking for search queries in image search engines by including imagery in your blog posts. This in itself can prove a substantial traffic driver.
The general consensus is though, that visuals in web content have a much higher engagement rate and aids the effect of any copy as it's just one way of breaking up the text into easily readable sections.
It is recommended to include imagery, especially for more lengthier pieces of content but it's not necessarily vital and isn't to say you can't rank well in organic search without images.
Social Media Today previously published a piece on some of the potential benefits of using images in blog posts. Whilst this piece only touches the surface really and is relatively basic, it gives some insight as to what benefits there can be from utilising visuals in blog content.