When and why do we use ellipses?

I just got asked this question:

Is there any reason why; in the Action menu on the Virtual Machine Connection window -  most of the actions are written as “Turn Off…” or “Shut Down…” whereas “Save” and “Pause” have no trailing “…”?

And then you compare it to Hyper-V Manager and there’s inconsistency between the two? For example it’s “Snapshot” in Hyper-V Manager but “Snapshot…” on the Virtual Machine Connection window.

What they are asking about are these menus in our user interface:

And there actually is a logical answer here.  If clicking on an option will cause us to open a new window or dialog – we put an ellipses (…) on the end of the command.  The reason for the difference in the Snapshot menu item is that when you select the option from the Virtual Machine Connection window; you will be prompted for a snapshot name.  Whereas if you select to snapshot from the Hyper-V Manager we will just give it an automatic name.

But… Uh… As I have been writing this post I have noticed that the Hyper-V Manager does not have an ellipses after the Reset command – and it does prompt you for confirmation.  That would be a bug.

Cheers,
Ben