Printed book layouts

New to printing books in Aperture (3.6)…

I appreciate that every Theme has a variety of (different) Layouts.

Presumably so that each page could (if I wanted) have a different Layout for the sake of variety.

And that the Layout for each page is selected from the black arrow which becomes visible when the page in question is selected…

But why do sequences of pages - once I've chosen a Theme - show multiple different Layouts?

Can't they all be the same; and I'll select an exception when I want one?

I can see why the dust jacket and title pages at the beginning need to be different. But why do some Themes suddenly have a 'Title' Layout on page 10, for example?

Following from that, how do I select a Layout which I like (e.g. '1-up Full') and apply it permanently to all the pages in my book, please?

Or am I missing how it's all supposed to behave?

TIA for any guidance :-)