Where’s @aidacra when you need him? He explains these things so well… 
Yes, it is just for if the Task Agent on the main server goes down. I think back in the earlier versions of 10 there were a lot of problems with the Task Agent stopping or getting hung up which would cause all other processes sent to it to fail/hang. So it was recommended to us to create at least one other Task Agent just in case. Here is a post that explains this in more detail:
Where are you located @ckrusen? Just wondering if you might be close enough to come to the MI/IN EUG to see @aidacra’s presentation which will cover some of these topics and best practices for SQL, AppServer, TaskAgent setups!