title: NSError objects with NSFetchedResultsControllers
body: <p>This is a simple one: I'm currently creating a new <code>NSError</code> object every time I perform a fetch on my <code>NSFetchedResultsController</code>. This occurs across a number of methods, so there are currently nine of them in my main view controller. Should I create one <code>NSError</code> as a property and use that, or is it more conventionally accepted to create a new one each time you use it?</p>
  
  <p>I'm guessing the advantage of creating multiples is that if more than one error occurs, you can get at both independently, but if this is unlikely to occur, is it acceptable to use a shared one for all <code>performFetch</code> calls? I'm learning a lot of programming convention and technique, so apologies if this is something of a non-issue, I'd just like to get some feedback on the more typical approach to using <code>NSError</code> objects in a variety of places.</p>