Two clientConnection.cs questions

I'm currently going through the common scripts line by line and I've come across two things I could use clarification on. They're probably pretty easy but here goes (and thanks in advance for any help):

1) I see that the actual message parameter is left as "" - so what is the purpose of making this messageClient call? If it's to tag the strings ahead of time, then why is the message parameter itself left blank? I notice a similiar call that sends the connection error but I don't understand that either. What am I missing?

// These should be "silent" versions of these messages...
         messageClient(%client, 'MsgClientJoin', "", 
               %other.name,
               %other,
               %other.sendGuid,
               %other.score, 
               %other.isAIControlled(),
               %other.isAdmin, 
               %other.isSuperAdmin);

2) These two lines are an error, correct?

$instantGroup = ServerGroup;
$instantGroup = MissionCleanup;

The second assignment nullifies the first. I know what $instantGroup is for, but which group should it be assigned to ...?