It is now necessary to have a working audio track to work with. The next stage of the program will be to create a fully timed-out animatic as the basic foundation of your film. Consequently, the timing and action judgments necessary will best be made by using the timings of your audio track. It isn't always necessary to have the final track to work with—to be honest, a guide track will often do. However, some kind of track, even if it is a piece of music with no dialog at all, is far more useful for working out scene cuts and animation timings than with using nothing at all.