It doesn't do anything when it's called, but your code to create the string gets called. This may be relevant in case creating the string is expensive. I had a case very recently where RACObserve signals (I had many of them) were calling `setName:` with the observed object, and calling description on that object was expensive (`-[MTLModel description]` turns out to be kind of expensive). In the end `setNameWithFormat:` was showing up as the # 1 CPU hungry method in the time profiler :)

Just a random comment, I don't think there's a way to avoid doing this work ON THE CALLER. As a side note, I "fixed" (avoided) this issue by overriding -description in my `MTLModel` subclass.