The roles you assign users for working with documents and questionnaires allow those users access to content in the workflow statuses that correspond with their roles. For example, an owner will see content items in the Draft status, a writer will see items in the Collaboration status, and an assignee will see items in the Published (documents) and Started (questionnaires) statuses. Which content items they can see in each of these statuses depends on assigned security levels, as explained below.
All Users. When a document/questionnaire is assigned this security level, all users with the roles mentioned above can see that content item in the workflow statuses they have access to, even if they are not specifically assigned to that item. For example, someone with the Document Owner role who is not a document's owner can see that document while it is in the Draft status, and someone with the Reviewer role who is not assigned to a particular document can see that document while it is in the Review status.
Restricted - High. With this security level assigned to a document/questionnaire, only those specifically assigned in one or more Properties Wizard steps (Writers, Reviewers, Approvers, Assignees) of that document/questionnaire have access to it. They can also access the document/questionnaire in any workflow status except archived. For example, someone assigned in a document's Approvers step can see that document while it is in the Draft, Collaboration, Review, Approval, Pending, and Published statuses.
Restricted - Severe. As with the Restricted - High security level, only users specifically assigned in one or more Properties Wizard steps of the document/questionnaire have access to it. However, they can only view that document/questionnaire when it is in the status corresponding with the Properties Wizard step to which they are assigned. For example, a user assigned in the Writers step can only see the document/questionnaire while it is in the Collaboration status.