I use the groove as I get out to 25 yards +. Learned this trick from a former F.A.S.T. guy. Good stuff, helps me stabilize my weapon, since I tend to overgrip with my strong hand during timed qualifications (been in law enforcement for awhile). I find this technique to be quick fix when under pressure, i.e. competition.
Now, here's something cool. Ever wonder who came up with this design? My reading points to Paris Theodore--creator of the ASP handgun. This story is that this design feature came about in/near 1970, but wasn't patented...? Below is an excerpt from one of several sites that state:
"Another striking feature of the ASP was its uniquely shaped triggerguard. The standard triggerguard was cut, and a hooked extension was heliarc-welded onto the pistol using a comparable alloy. The design was patented as a “forefinger pocket” and aided in a finger-forward, two-handed grip. For improved access, the forward half of the triggerguard was reduced in width by 50 percent—a change that tailored to right- and left-handed shooters." (found this excerpt at personaldefenseworld. Not enough posts yet to post up link)