What is on the list
The items are the reasons files get bounced by printers, grouped as pages (page size, safe area, bleed, page count, spreads), files (resolution, flattening, fonts, TrimBox), colour (colour mode, rich black), cover, and delivery (file naming, proofs). Page size, resolution and safe area are written with your own numbers, and where a tool can verify an item there is a link to it. Items the project settings can decide on their own are ticked or flagged automatically. Those follow the settings, not a tick: a page count that is not a multiple of four stays open until the count changes.
Inside a project, Save checklist progress stores your ticks with the project and they come back next time. Standalone, your ticks stay in this browser. Background reading: preparing a print PDF and RGB vs CMYK for comics.