Final Cut Pro 3: AE Plug-in Performance With External Video
Certain third-party After Effects plug-ins can take longer than normal to update in Final Cut Pro each time a settings change is made to them in the Viewer if a video monitor is connected through FireWire. Because filters in Final Cut Pro must render for both the RGB screen as well as for the video out signal, you can eliminate this delay by setting External Video to Off (Command-F12).
Symptom
The watch cursor appears for a long period every time a setting is changed in a third-party After Effects plug-in.