When to use SYS_CONTEXT function

The SYS_CONTEXT function allows you to define a namespace and then place parameters
within it so that they can be retrieved for use at a later time. The general syntax for the use of
SYS_CONTEXT is as follows:

SYS_CONTEXT('namespace','parameter'[,length])

A namespace can be any valid SQL identifier, and it must be created using the CREATE_CONTEXT
statement. The parameter must be a string or evaluate to a string, and it must be set using the
DBMS_SESSION.SET_CONTEXT procedure. The call to SYS_CONTEXT with a valid namespace and parameter will result in the return of a value that has a VARCHAR2 datatype.
The USERENV namespace is automatically available for use because it is a built-in namespace
provided by Oracle. The USERENV namespace contains session information for the current user.