The bulk of a publishing agreement is concerned with 'primary rights': the rights that you as the author assign to the publisher to allow them to publish the book in its primary editions (for English-language publishers, that's print, ebook and audio rights in English).
Subsidiary rights are those that are not directly exploited by the publisher themselves, but sub-licensed to others for specific purposes. The most common of these is translation: at Practical Inspiration we have a rights team who actively pitch our titles to foreign-language publishers around the world. We also regularly license audio rights and serialization rights - sadly no-one's taken an option for a movie on one of our titles yet, but we live in hope.
By granting these rights exclusively to your publisher, it means they can be sure no-one else is cutting licensing deals without their knowledge (if, for example, we licensed an exclusive deal to a German publisher only to find there’s a competing German version which you'd arranged separately, that would be a problem…). If you're working with Practical Inspiration and there's a subsidiary right that you'd particularly like to retain - for example if you DO have contacts in a German publishing house and you'd like to arrange to publish the German translation of your book directly - then just let us know and we'll carve that language out of the agreement so that you retain the right to do so.
The author's share of revenue from subsidiary rights is typically 50%.