"Custom log views provide you with an advanced and granular way to control access to your logs data. For example, consider a scenario in which you store all of your organization's logs in a central Google Cloud project. Because log buckets can contain logs from multiple Google Cloud projects, you might want to control which Google Cloud projects different users can view logs from. Using custom log views, you can give one user access to logs only from a single Google Cloud project, while you give another user access to logs from all the Google Cloud projects."
Regarding _Default view: "Cloud Logging also creates a view for the _Default bucket called _Default. The _Default view for the _Default bucket shows all logs except Data Access audit logs.", be noted it shows "all logs"