When it comes down to writing it is a matter of what needs to be done right now and not later.
Sometimes it is as simple as: Do I write my blog post of edit my book?
There is not a lot of pros and cons to this sort of question, it is more a matter of deciding what needs to be done right now and not later. Now, if your book needs to be edited by tomorrow morning, your blog post can wait. Of course if you have a month to finish those edits, then you should be okay to write that blog post.
Remember editing and writing on a blog is somewhat like housework, these need to be done, and they need to be done each and everyday.