in a fight you already have something set.... you are adding another step for every spell, another split second decision, then keystroke which completely nullifies that nanosecond you achieve from target que over just experienced play. To each their own for sure, but I feel that it is more of a detriment than a plus if you are proficient with spell timers already.
I have last target key then a Q last target on mouse wheel along with a Q self on wheel along wish mouse side button clear Q targets. If you cast FS or EB and slam that key you'll get used to it and clear Q. I don't use smart target which I am sure I should... If you're killin peeps and you're happy then don't change