I just created a comparison layout to compare file sizes between InDesign and Affinity Publisher. The difference in sizes is enormous! A four page document with one large image (spread) and some text with an image calculates out to this:
Affinity Publisher Layout (embedded images): 186 MB
Affinity Publisher Layout (linked images): 165 MB
Adobe InDesign Layout (linked images): 2.07 MB
Affinity Publisher Layout (ZIP file): 94.6 MB
What is making the file sizes so bloated?
My understanding and explanation of this issue was incorrect, sorry. Linked images/resources are meant to make smaller .afpubs than when embedded. Embedded documents are embedded (with a preview for render speed). Linked documents will store a preview of the linked file, but currently due to a bug they store too many previews and increase the filesize. Currently linked files also store the file (as well as too many previews), but this is a work in progress.
I will try to be better informed before I post next time.