You would like to have maximum control over how separate tasks run in your application. For instance, you would like to run a long calculation requested by the user while freeing the main UI thread to interact with the user and do other things.

Utilize threads in your application, like so:

- (void) downloadNewFile:(id)paramObject{
  
  @autoreleasepool {
    NSString *fileURL = (NSString *)paramObject;
    
    NSURL    *url = [NSURL URLWithString:fileURL];
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    NSURLResponse *response = nil;
    NSError       *error = nil;
    
    NSData *downloadedData = 
    [NSURLConnection sendSynchronousRequest:request
                          returningResponse:&response
                                      error:&error];
    
    if ([downloadedData length] > 0){
      /* Fully downloaded */
    } else {
      /* Nothing was downloaded. Check the Error value */
    }
  }
  
}

- (void)viewDidLoad {
  [super viewDidLoad];
  
  NSString *fileToDownload = @"http:/....