App Class v/s CI

At somepoint in the implementation or maintenance project; you would face this Q.
Whether I should go for readily available CI or dig into complex App Class and find the right method/Class to fulfill my requirement.
PeopleSoft CRM uses a number of CIs in the out-of-the-box product for application specific purposes. As a programmer; you would have found that the out of the box CI for CDM was too slow.Also, there is limited control the programmer has over the processes triggered by the component interface.
Application classes have been provided as a solution for the performance problems. Application classes are provided out of the box in CRM8.8
In traditional in-house built PeopleSoft applications, it is recommended that the use of CI’s be replaced by referencing the methods in the Application Classes directly. Keep in mind that application class programming requires a new skillset.
Application classes can be used to simulate CI functionality. In the code where we instantiate CI to invoke a component an application class logic could be invoked instead. The developer should keep in mind that this is not a direct replacement, however, because the way you invoke applictation class methods is different than the way you invoke CI methods.