This is relevant not only in the context of books and blogs, but also for the shorter forms of reading that we do more often like HN or Reddit comments, tweets etc.
One way to think about it is that reading on the internet, no matter how casual, is like scattering seeds on the soil of your mind. Some of these seeds will grow into trees and influence your actions and decisions, whether you're aware of it or not.
Like all things, the effectiveness of the above depends on a good balance i.e. distraction by simply jumping amongst topics vs. concentrated thought on any one idea at a time. They are not the same.
In Hindu/Buddhist philosophy there is a concept of "Samyama"(https://en.wikipedia.org/wiki/Samyama) and "No-Mind" (one aspect - https://thetealetter.com/japanese-tea-ceremony/mushin-discov...). What this means is that when you are reading/working/etc. on something, your mind is completely occupied with it to the exclusion of everything else. Even if that activity is of only a very short duration your mind is completely possessed by it and when it ends, your mind drops everything to do with it and moves on to the next activity to occupy itself completely. This is the basic idea behind meditation/mindfulness/etc.
One way to think about it is that reading on the internet, no matter how casual, is like scattering seeds on the soil of your mind. Some of these seeds will grow into trees and influence your actions and decisions, whether you're aware of it or not.