In this doc it says: "Cached interstitials are deleted from memory after they are shown. If you plan to display another interstitial for a particular location, you should cache that location again"
page 3 / caching
But in every example I met there's the caching only for once, even in the chartboost example project
So the question is: should I use [cb cacheInterstitial:@"Pause screen"]; only once at the beginning or should I use very time I showed a cached ad?
Displaying cached ads is definitely the best user experience, so I'd recommend doing it every time!
If you look down to the - (void)didDismissInterstitial:(NSString *)location method in the example project, you'll see that they're caching again.
This delegate method is fired every time an interstitial is clicked or closed, so adding cacheInterstitial:location here will immediately recache an interstitial for the location every single time!
Don't forget to add cb.delegate = self; after initializing the cb object to ensure that the delegate methods work properly.
Full Disclosure: I work for Chartboost.