When resizing a dashboard panel, the default action is to overlap with panels beneath. I'm not sure of when that use case would be preferred over rather shifting down or across a panel that conflicts with the panel boundaries you are moving around.
For example, if I resize a panel and make it longer downwards (increase the height), I expect the panels beneath the one I' resizing to shift down automatically.
Would like to also see this functionality expanded to include ability to select multiple panels and cut and paste them elsewhere in the dashboard for easier reordering. Updating dashboards is quite cumbersome due to the lack of some basic features like this one and the limited number of dashboard filters which I also voted for.