Before inviting a collaborator to work on a timeline with you, you might want to see the timeline exactly as they will see it first.
One common use case might be you're inviting a groom to make some edits, but you don't want him to see the surprise you are planning for him. You do that by marking the individual item as hidden. (See how to do that here). But once you have hidden the item, you find you want to triple check that it is not showing up on his timeline.
Here's how to "view as":
Go to the timeline you are working in
Go to the Collaborate tab
Click the settings gear icon
Click on the three little dots of the collaborator you want to triple check
Click "View As"
A new tab will open that shows you the timeline exactly as your collaborator will see it when he or she is invited. That means that anything you have hidden from the collaborator will not be seen.
Here's a quick video tutorial for you visual learners: