Sometimes I catch myself using a looser grip when I'm making individual, long-range (or very precise) shots. Even for a single fast shot, there is an incentive to spend less time establishing a grip with good recoil recovery capability.
The danger in using such a grip, though, is that in defensive gun use, you never know ahead of time which shot is the last one you'll have to. You determine the last shot by observing your assailant's reaction. When the threat ends, you're done. You can't know this prior to firing the shot, so you must always take the extra time, tens or hundreds of milliseconds, to establish a firing grip that is optimized for delivery of follow-up shots.
The temptation to build a grip optimized for a single shot is particularly strong when you are in a situation where there will be no recoil to test your grip: dry fire. Often, in dry fire you work only against the timer. The saying "you are what you measure" is especially important to bear in mind here. The temptation to optimize your draw, presentation, grip, and trigger press against the timer alone is strong, especially as you push yourself by trimming tenths of a second off your par time. An honest evaluation of your sight picture and grip as the trigger breaks is just as important, but far more subjective.