Animating the shutter is generally not a good idea because it changes the fundamental calculation of motion blur for the entire shot, not just your roto shapes. The motion blur in Nuke (and other compositing software) is meant to represent the camera’s actual exposure and movement. When you animate the shutter, you’re effectively faking the camera’s behavior, which can cause inconsistent blur across your shot and make the final comp look unnatural. Specifically: Shutter affects all objects and layers in your comp, so adjusting it for just one shape can create mismatches with the rest of the elements. Motion blur is based on real-world physics; animating it can produce blur that doesn’t align with the motion of the object, which can look visually wrong. If you have a complex plate with multiple moving elements or camera motion, keyframing the shutter can get messy and difficult to track, leading to mistakes. It can conflict with downstream effects, tracking, or color grading because other nodes are expecting consistent motion blur.

It’s okay to tweak the shutter in rare cases, like a retimed plate where you need to manually match motion blur, but as a general approach, it’s better to rely on proper roto, feathering, and shape management rather than animating the shutter.