It would be nice if I could create a drag interaction that would allow me to stop at any tween state between the two targets. If I have a slider, I could stop dragging at any point along the slider. If I have two sizes for a component with a dynamic layout, I could resize it to any size between the two targets> Get that this will not work in every case, but there are some cases where it makes sense.
You could also attach the drag to a range of property values and let me drag to any value within the range. If I use the slider example, I could define the start and end positions and drag the X, Y, Width, or Height values between start and end range values. Stopping at any value in between the start and end values.
okay, you can preserve scroll position, but there is still a difference between scrolling a rectangle and dragging between to a tween state between two variants states. There are a lot more possibilities with that option. Image resizing a window in the OS to any size while the content dynamically updates the contents (like a web browser would do), but not being limited to predefined sizes.