There are two different types of performance enhancing options that can be turned on in the project that will improve your project loading speed. The in-memory options allow for significantly faster calculation of results in the StoryTeller and Cross Table Tool 2.0. In most cases, the calculation will be fast enough for an efficient user experience that will not require pre-generated StoryTeller reports.
In case of a very complex and large project, data may be prepared in advance and stored into the system to gain faster access to completed modules and the data that has been processed. In this case you can use data pre-generation. The pre-generation is basically saving a lot of time as it stores your tables and charts (along with combinations) so they can be called in immediately.