Question

We all know about log, ok, but why should we consider the «Logger» class a singleton one? What happens if we make it as a normal non-singleton class?

Answer 1

I found this here on the IBM site. It explains the usage of a Logger Singleton class quite well.

A classic example of a true singleton
is a logging service. Suppose we have
an event-based logging service: Client
objects request that text be logged by
sending a message to the logging
service. Other objects actually log
the text somewhere (console, file,
whatever) by listening to the logging
service for these logging requests and
handling them. First, notice that the
logging service passes the classic
test for being a singleton:

• The requesters need a well-known object to which to send requests to
  log. This means a global point of
  access.
• Since the logging service is a single event source to which multiple
  listeners can register, there only
  needs to be one instance.

Here the link: Use your singletons wisely

If you wouldn’t use a singleton class you would have to deal with the synchronisation (writing to a file, or whatever stream you use) between these different logger instances. So its much easier, when you just have one global Logger instance.