I find that with large boards i tend to be zoomed out and when you put in notes or docs or images cards etc they are too small and often especially with a trackpad it is a bit of a mission to click the corner and and resize manually. Often i might have to zoom in to be actually able to select a corner of the sticky or image to make it bigger.
I think an easy work around would be instead of a s,m L option for resizing, to have a size up or down in the bar that comes up when you make a sticky. So if you are at a zoomed out macro level you could resize it to the right size at a click of a button instead of zooming in expanding then zooming out.