They will be hidden (i.e; they won't show up in the AP, but the QMC will still list them).
Bookmarks can always be created, whether or not you enable this checkbox.
Yes, you will disable server objects system-wide (i.e. for all users and all documents), even if they were previously enabled for specific documents. [Edit] Sorry about that. Levi's right. Your screenshot shows the document-related setting which enables/disables server objects for this particular document only.
In what area? You will effectively disable QlikView self-service BI.
The global setting is called "Allow Server Objects". Disabling this setting will block all users from creating any server objects on any document and will hide all existing server objects.
The document-specific setting is called "Allow Creation of Server Objects". Disabling just this one (while the global setting is still enabled) will only block users from creating new objects for this document. However the existing ones will stay put and remain visible in the AP.
I don't seem to be able to disable the creation of bookmarks in the AP, whatever the combination of checkbox settings...