Inserts and sends can be dragged and rearranged in mixer window, but it's not possible currently to leave empty space between them. From a organised standpoint there would be multiple benefits from allowing to do so:
1. Putting EQ plugin (for example) on a same row horizontally on each track, allowing a quick A/B (on-off) on multiple tracks simultaneously. If all similar plugins are lined up across session, it's easier to see overview whats happening mixing wise.
2. Grouping inserts in a fx chain for a better visual. For example leaving space between utility plugins and sound shaping plugins on a track.