While using the GetUsers web service call with the options Sections-none, the default data gets returned with the requested data, potentially slowing the operation.
'Groups & Users' option for multi-user fields should provide elevated functionality with respect to 'Individual users' option and that is not the case as it doesn't provide the [Members Of:] functionality.
When there are more than 1000 user selections for the application admin/web admin to sort through for setting a default user field value, the admin tool can hang and stop responding.