Often there is a misconception about how Audience Targeting in a List or Document Library works; lets consider a scenario where –
Administrator has setup an Audience on Shared Services Provider with following rule.
Account Name (Property) = Contoso\Adam
1) Users “Contoso\Adam” and “Contoso\Julie” both have Contributor rights in a Document Library. Administrator enables Audience Targeting from List Settings > Audience targeting settings.
2) Document Library has 4 documents out of which Administrator enables Audience Targeting on 1 document (Deals.docx)
Administrator expects this document should be only visible to Contoso\Adam user [Either in Document Library or in Document Library Web Part] which is an incorrect expectation. Contoso\Julie will still continue to see the document both in Document Library and Document Library Web Part.
For these kind of scenarios, it would be wise to use item level permissions which will not allow Contoso\Julie user to see the document in either Document Library or Document Library Web Part due to SharePoint Security trimming.
So, you must have a question now… What is the use of Audience Targeting in a List / Document Library?
To display the content of a Document Library based on audiences, you need to use the Content Query Web part. In the properties of the Content Query Web Part you can specify to use the audiences to display the content (apply Audience Filtering).