I can think of a few usage modes for the developer to choose from (and possible let the user choose from):
1. When dragging multiple day events they are moved relatively (i.e. if I drag events of the 17th and 18th and drop them on the 20th then actually drop on the 20th and 21st)
2. when dropping multiple day events they are all dropped on the same day 
3. I display multiple resource route optimization. The user wants to take Alice's tasks 1 & 3 and also Bob's task #5 and drop all of them to Charlie. They all should have the same resource assigned to them (when dropping on a resource even for multi resource selection the new resource should be the same for all tasks)
4. When dropping multi day tasks on the AllDay slot, they each should become an all day event (again dividing into two options: all on the same day or relative)

I saw you asked for a usage scenario so here is my simplest usage scenario: I display a proposed daily schedule of 10 resources over 100 tasks after I made route optimization on them. the user want to take a few tasks and move them from one resource to another. instead of moving them one by one he should be able to mark all of them and drag them to the required resource

What are we waiting for?
This is a "must have" feauture for the Scheduler.
Please don't make me have to use this product for this:
http://demos.devexpress.com/ASPxSchedulerDemos/ClientSide/AppointmentsSelection.aspx

Regards, Thomas

Please make it so...