title: CCSpriteFrameCache release strategy
body: <p>As far as I understand the <code>CCSpriteFrameCache</code> gets filled when creating sprites from files and spritesheets and should be clever enough to purge unused frames when getting out of memory.</p>
  
  <p>My question is: in my app should I worry about manually releasing unused frames as soon as possible or should I just rely on the cache to purge itself when necessary?</p>
  
  <p>Is there any side-effect (like overall performance issue of the system or of other running apps) in letting the cache grow until getting memory warning?</p>