I sometimes end up in the situation where I close the laptop lid and, instead of suspending, a shell global dialog appears on the (closed) display, informing that other users or some application are inhibiting suspend. [1]

Right now it just happened to me that I had a VT session (of my same user) open, but it's not always reproducible that way (e.g. I killed the VT session, closing lid actually suspended, logged in again at the VT and I can still suspend).
I think (but am not 100% sure) sometimes I also saw this with no VT sessions open, and the dialog would say that an application is inhibiting suspend, even if I had no applications open that appeared to do so.

In any case I think closing the lid, as an user physical action, should *never* trigger a confirmation dialog like that, and should just do the action, even more so because not suspending in that scenario can severely damage the hardware.

[1] As a side-effect bug, the modal dialog appears on top of the lock screen, and after dismissing the dialog or resuming, pressing Escape doesn't raise the curtain anymore, nor pressing other keys make the curtain bounce like it normally happens.