Clarify how control flow is handled in CATCH blocks

doc/Language/exceptions.pod6

@@ -47,7 +47,8 @@ problem.
 
 =head1 Catching exceptions
 
-It's possible to handle exceptional circumstances by supplying a C<CATCH> block:
+It's possible to handle exceptional circumstances by supplying a
+C<CATCH> block:
 
     die X::IO::DoesNotExist.new(:path("foo/bar"), :trying("zombie copy"));
 
@@ -57,18 +58,22 @@ It's possible to handle exceptional circumstances by supplying a C<CATCH> block:
 
     # OUTPUT: «some kind of IO exception was caught!»
 
-Here, we are saying that if any exception of type C<X::IO> occurs, then the
-message C<some kind of IO exception was caught!> will be sent to I<stderr>,
-which is what C<$*ERR.say> does, getting displayed on whatever constitutes the
-standard error device in that moment, which will probably be the console by
-default.
+Here, we are saying that if any exception of type C<X::IO> occurs, then
+the message C<some kind of IO exception was caught!> will be sent to
+I<stderr>, which is what C<$*ERR.say> does, getting displayed on
+whatever constitutes the standard error device in that moment, which
+will probably be the console by default.
 
-A X<C<CATCH>|CATCH> block uses smartmatching similar to how C<given/when>
-smartmatches on options, thus it's possible to catch and handle various
-categories of exceptions inside a C<when> block.
+Note that the match target is a role. To allow user defined exceptions
+to match in the same manner, they must implement the given role. Just
+existing in the same namespace will look alike but won't match in a
+C<CATCH> block.
 
-To handle all exceptions, use a C<default> statement. This example prints out
-almost the same information as the normal backtrace printer.
+A X<C<CATCH>|CATCH> block places any exception thrown in its topic
+variable (C<$_>), thus it's possible to catch and handle various
+categories of exceptions inside a C<when> block. To handle all
+exceptions, use a C<default> statement. This example prints out almost
+the same information as the normal backtrace printer:
 
     CATCH {
          default {
@@ -81,9 +86,18 @@ almost the same information as the normal backtrace printer.
          }
     }
 
-Note that the match target is a role. To allow user defined exceptions to match
-in the same manner, they must implement the given role. Just existing in the
-same namespace will look alike but won't match in a C<CATCH> block.
+While this is a very common pattern, it is not strictly necessary to use
+C<default> or C<when> in a C<CATCH> block. This is done to prevent the
+control flow in one from reaching its end where, unless the exception
+has been L<resumed|#Resuming_of_exceptions>, the exception will continue
+to be thrown.  Allowing this can be used for logging purposes, for
+instance:
+
+=for code :skip-test<creates a file>
+# In the outermost block of a script...
+my IO::Handle:D $log = open sprintf('logs/%d-%d.txt', $*INIT-INSTANT, $*PID), :a;
+CATCH { $log.printf: "[%d] Died with %s: %s$?NL", now, .^name, .message }
+END   { $log.close }
 
 =head2 Exception handlers and enclosing blocks