If you give very limited policies to your contributors, and if they want to preview a content, you'll need to give access to content/versionread with (at least) a limitation on status=draft.

Then, the contributor who uses the "preview" button in left column, will see the preview (works as expected).

Issue : if he uses the link (introduced with ezautosave) at the top right corner, then he will get an error telling him he does not have the right to do this (and the siteaccess being displayed is the admin one, even if you select another one in the dropdown).

Workaround / hints for debugging : the issue disappears by giving access to content/versionread without any limitation (which is something that the admin might not want)