title: Why set customCell property to nil using UINib
body: <p>I'm looking at some Apple sample code using the UINib method for cellForRowAtIndexPath for UITableView:</p>
  
  <pre><code>-(UITableViewCell*)tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath {
          static NSString *QuoteCellIdentifier = @"QuoteCellIdentifier";
          QuoteCell *cell = (QuoteCell*)[tableView dequeueReusableCellWithIdentifier:QuoteCellIdentifier];
          if (!cell) {
                  UINib *quoteCellNib = [UINib nibWithNibName:@"QuoteCell" bundle:nil];
          [quoteCellNib instantiateWithOwner:self options:nil];
          cell = self.quoteCell;
          self.quoteCell = nil;
  </code></pre>
  
  <p>I don't quite understand the last two lines</p>
  
  <pre><code>        cell = self.quoteCell;
          self.quoteCell = nil;
  </code></pre>
  
  <p>Can someone explain what is happening in those last two lines?  thanks.</p>