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“Author Base” value shouldn’t match any other slug in your site. That would cause redirection issues. So, you cannot type in something like “writers” if you already have or plan to have a page named “Writers”, which default slug is/would be “writers”.
It make senses to set an “Author Base” in the singular, rather than the plural.
Molongui Authorship Pro allows you to customize different aspects of author archives, like permalink structure or the page title. You can even disable author archives if you don’t need them. But perhaps the most relevant feature that Molongui Authorship Pro offers is guest author archive pages.
Guest author archive pages are regular author archives but for guest authors instead of users.
Guest “Author Base” could match User “Author Base”. Both of them are considered as “Authors”, so it makes sense to keep the same URL structure for both.