AddPageAndCreate runs the B4XPage_Created, so "often" (always?) loads the layout.
True. Assuming that you are loading the layout in B4XPage_Created then it will always be loaded.
When you add a page with AddPage, B4XPage_Created will only run when the page is first shown (lazy loading).
Advantage: no performance impact when app starts.
Disadvantage: you cannot interact with the page views before the page is first shown.
AddPageAndCreate - adds the page and call B4XPage_Created
Advantage: no need to worry whether the page was already created or not. It will be ready immediately.
Disadvantage: if you are creating many pages when the app starts then it can slow down the app.