Using screen modes and Presentation in Layout by Zaweba
Normal, Preview, Bleed, Slug and Presentation screen modes in Layout by Zaweba, and when each one helps you judge a page or show it to someone.

Screen modes change how Layout by Zaweba draws the page, without changing the document. The same spread can be shown with all its working marks, as clean as a printed sheet, with the bleed area included, with the slug included, or full screen one spread at a time. Picking the right one at the right moment makes it much easier to judge what you've made.
The five modes
Normal is the working view. Guides, frame edges, margins and the pasteboard are all visible, which is what you want while you're placing and aligning things.
Preview hides guides and frame edges. The page looks like the finished piece, trimmed to its edge. It's the view for judging balance, white space and how a spread reads as a whole, because the scaffolding no longer catches your eye.
Bleed shows the page plus its bleed area, without the working marks. Use it to check that pictures and colour panels that should run off the edge really do reach far enough. A background that stops a hair short of the bleed shows up straight away here.
Slug shows the page with its slug area, which is where job information, notes for the printer or sign-off details live outside the trimmed page. Use it to check that information is where it should be and isn't straying into the page itself.
Presentation is full screen, one spread at a time. Everything else in the window disappears and the spread fills the screen, so it's the mode for showing a layout to a client or colleague, or for reading through a whole document as a reader would.
A rhythm for using them
A good habit is to flick into Preview every so often while you work. Guides and frame edges are useful, but they make every page look busier than it is, and they hide problems such as two pictures that are almost but not quite aligned.
Before sending anything to print, go through in Bleed mode. It's the quickest visual check that the bleed is filled where it should be. Live preflight in the app will flag bleed problems too, but seeing them helps you understand what needs fixing.
Use Slug at the end of a job if you've put notes there, so you're sure they're complete and readable.
Presenting work on screen
Presentation turns Layout by Zaweba into a simple viewer. Step through the spreads and talk someone through the design without menus and panels in the way. It's also a good way to proofread the flow of a magazine or brochure, because seeing one spread at a time at full size is closer to turning pages than scrolling is.
Before you present, run through the document in Preview first, so that any stray frame or forgotten placeholder on the page is caught while there is still time to fix it.
Common slips with screen modes
The main one is forgetting which mode you're in. If you can't see your guides and wonder where they went, you're probably in Preview. If the page looks bigger than it should, you may be in Bleed or Slug mode.
Another is trusting Preview alone for print. Preview trims to the page edge, so a picture that falls short of the bleed can look perfect there. Bleed mode is the one that shows it.
Screen modes cost nothing to switch between, so use them freely. A minute in each before a job goes out is time well spent in Layout by Zaweba.