In eZ Recommendation Installation procedure documentation page, there's a mistake on the module permissions:

Grant access for the ezrecommendation module
3. Click on the "new policy" button
4. In the "Module" combo box choose "ezrecommendation"
5. In the "Function" combo box choose request.
6. Then click on the button "Grant access to all functions"
7. Click the save button

This is confusing.
If you choose Request Function, it makes sense that you Grant full access to that function.
If you Grant access to all functions, as explained in the procedure, it makes no sense to choose Request Function.

Please clarify if it's necessary to grant access to all functions for anonymous, or if it's necessary only to grant only full access to Request Function

Apply the same above process for role "Member" and for all other role groups that you wish to provide recommendations. Usually Anonymous and Member are enough.

This is also confusing. The member group already has anonymous role by default, yet the documentation indicates both should be changed.
It would make more sense to create a new recommendation role and assign it both to anonymous and members groups, leaving the other roles untouched.