I can get a firing grip on it while it is still in there, summer or winter, and nobody around me is the wiser.
I cannot get a firing grip on the Glock in my JMCK IWB belt holster under whatever concealment I am wearing without telegraphing a whole lot to the world. Some years ago @Mas taught me that, and helped me understand the advantage it offers, both in stealth and the advantage having that firing grip has on the actual speed of response if it has to come into play.