This is something that would be very useful to me, but I can't find the keyboard shortcut in the manual.
If I have a whole bunch of event copied and just want to copy them on the same level than a subevent.
Or if I want to make some event the subevents of what's in the clipboard, I could just create a blank sub-event above, copy my clipboard event below it, delete the blank sub-event, then move the previously existing events to subevents of what I just pasted.
Not sure this is clear, but anyway, this would definitely save time in the event sheets.