Nice to have, handy, down the road. Not a must have right now.
Scenario where I felt the need the most was when I had to set a repeat on multiple items. As there are no repeating projects (yet? see: Repeating projects) all items in several projects had to be made repeating…one…by…one…
Yep, this is certainly a nice to have.
Also yes, multi-select by itself does nothing.
What you want is bulk edit, so I’ll rename this and add to the backlog.