The call you showed runs the block on the main thread. That aspect may be crucial. Does the code this is part of run on a different thread/queue?

Also, it can often be very useful to defer some code until after the current event completes; this is often called a “delayed perform” because the old school way to do it is by calling -performSelector:withObject:afterDelay:. An async dispatch to the current queue is the moral equivalent. In the case of this statement, I couldn’t tell you why this is useful without knowing more about the code overall.

—Jens