BPF - 2 controlling applications?

What is the use of controlling application in the Define BPF tab ?

My controlling application in BPF is LegalApp presently becoz I am loading the TB in this applic. and also running some validation reports. As second step in BPF I need to put input schedule to accept exchange rates. However, the input sched is created in Rate application and am not able to bring this into my BPF whose controlling application is set LegalApp. Please suggest how to use input sched created in different application (other than controlling application ) in my BPF

andy