Talk:Hotkeys and commands/@comment-70.72.55.39-20101130054731/@comment-1699463-20101130200404

It's a dynamic cast that is dependent on the unit under your cursor. If it's a friendly spell and you're over a friendly unit, it casts it on that unit. If you're over an enemy unit, it self casts. Typically it's used for self casts such as heals and shields, since finding and selecting yourself wastes time.