iOS setDictionary: vs. dictionary = newDictionary

[l0uismustdie]

Hello. I am trying to trim the memory usage of my program down and am wondering if there is a difference between these two lines:

returnDict=[self fetch:memory andIP:IP];

and

[returnDict setDictionary:[self fetch:memory andIP:IP]];

It seems like I should use the second line...but does it really matter?

Thanks