I read some scary comments here. (By Blog page, he means the Posts page in the reading settings.)
The Blog Page gives out several indicators to social sites and Search Engines that it’s a Blog. […] In fact, WordPress requires a Blog page to be available. Failing to do so may cause bugs in some plugins and themes, and even within WordPress itself. […] The Blog page is a reserved item within WordPress. Many WordPress functions and queries are written around this item.
Is the Posts page really required? Can problems with plugins or Google occur if I leave it blank?
(Reason for asking: I want to use a parent category “blog” instead of a Posts page.)
Technically you don’t need to include a posts page on your site. Plenty of sites consist of just some pages and no posts at all.
However, Google uses the posts pages to find links to your individual posts. If there is no such page you will need a different structure to guide Google (for instance through the menu, by including a dropdown of your child categories). Given that Google’s algorithms are secret I cannot know whether using an uncommon navigation structure is better or worse for seo.