I'm working with symbols within tweens. When I insert a new keyframe within a sequence, like in a motion tween for example, it shows up as a small diamond shape rather than a dot. Why is that, and how do I change it? Because I want to make breaks within the sequences so I can fine tune positions and rotations.
You could think of dot being a key frame of everything, and a diamond being a keyframe of some things. If in a motion tween you happen to key frame everything, it's still a diamond. But that aside, with classic tweens you can only tween everything between keyframes. With Motion tweens you can tween one thing over some frames, and a different thing over a different range of frames.
It's not a layer thing. If you have a reason to need to tween different attributes over different frame ranges, then use a motion tween. If on every keyframe everything changes, then you may as well use a classic tween, and get the dots.