The "global" Logger object is provided as a convenience to developers who are making casual use of the Logging package. Developers who are making serious use of the logging package (for example in products) should create and use their own Logger objects, with appropriate names, so that logging can be controlled on a suitable per-Logger granularity. Developers also need to keep a strong reference to their Logger objects to prevent them from being garbage collected.
From here (don't look at the fact that the field is deprecated, I just wanted to point you to a valid explanation).
Normally, when enabling logging in an application, you define more granular loggers, usually per Java packages or classes.
If you do not want to do that, you can use this global logger, which will handle all logging statements, no matter the library, package or class they are contained in.