Chronological posts reverses the default post order throughout your site to be chronological instead of reverse-chronological. This can be useful for sites displaying historical content, journals, books, etc. where the content is intended to be read chronologically (typically, it works well for any sites where the entire content of the site – every post – is intended to be read sequentially). It is also useful for archived sites, preserving the history of posts in a sequential format, oldest to newest.