I posted this about a month ago but it was within another thread and was likely missed, here it is again:
See that shadow warg near top left, I summoned it off the battle grid. It was the weakest creature in my army so all the enemies want to kill it but can't reach it and I can't move the shadow warg either. So I killed these thing that are about 3 times as strong as me from a distance, as once they reached the edge of the grid they stopped moving.
When I aim the summons into an unreachable area I get the symbol that I can't summon there but a mouse click still allows the summons. If that creature gets the aggro, all the enemies become sitting ducks for long range attacks.
PS: I haven't tested it but I wonder if the teleport spell would allow a hero there too