The main reason is simplification. When you’re working with a team or if it has been awhile since you looked at the file. Trying to figure out what has been animated and what hasn’t slow you down. Also when you start animating several objects they will be in the way and clutter up the dopesheet/graph editor. Another reason is if you start doing reusable animations they can cause problems and if you’re not in the habit of cleaning up unused channels this will become something that slows you down. Memory and file size are relatively small and aren’t that much of an issue. Unlike zero weights on an Armature.
