The significant majority of the people I've helped train over the years I've served primarily as a LE firearms instructor have been ... LE. Sure, I did spend 10 years during that time also doing occasional some teaching of some small numbers of private citizen shooters (not more than a few hundred), but primarily it was LE.
That being the case, it was important that they be able to demonstrate the ability to shoot 1 & 2-handed, and using their "off" (non-dominant) hand, if necessary.
Naturally, the importance of obtaining accurate hits on the
intended threat reinforced the importance of techniques that were geared toward better potential accuracy, which meant understanding the value of 2-handed shooting at distances growing outside "arm's length", and especially if a precision (cranial vault) shot were needed, so the handgun was stabilized to maximum degree possible for the circumstances.
1-handed shooting can quickly demonstrate to a shooter (and their instructor) whether the shooter is successfully controlling and driving the gun, or whether the gun's recoil is over-whelming the shooter's mechanical ability to obtain consistently accurate hits.
Personally, having come up through LE shooting using a Magnum service revolver, I tend toward the importance of the master hand/grip being maintained for both 1 & 2-handed shooting.
That means the support hand
supports the master hand's grip, but doesn't interfere with it or require an "adjustment" of the master hand's grip in order to shoot 2-handed. My primary/master hand grip remains the same whether shooting 1 or 2-handed, as outside of known range conditions I won't know in advance whether I'm going to be required to defend my life (or that of an innocent 3rd person) using 1 or 2 hands. That master hand grip and control of the handgun needs to be maximized in anticipation of any and all circumstances.
I've usually liked how Mas describes this sort of thing relating to critical influences involved with a grip technique. Here's one of the articles I rather liked:
https://www.backwoodshome.com/how-to...un-accurately/
Now, if someone has the ability to know in advance whether or not they'll be able to use a 2-handed grip (controlled range drills or gaming venues)? Well, it may not be important to them whether they've reduced their reliance on the maximum control exerted and maintained by their master hand, and that's fine.
If I may have to suddenly fight with that handgun, though, and it's not points potentially lost, but my life? Well, suddenly that "60" part of the 60/40 2-handed grip might start to look like less of an advantage if there was suddenly no "40" available to help stabilize and utilize that "60".
Think you'll "automatically" be able to adjust your master hand's "60" grip back to a "100" grip under the stress of a deadly force situation? Especially if you're injured or it becomes critically important to suddenly "multitask" the use of support hand for something else?
And while we're thinking about things we may never wish to think about ... How's your "100" grip using your support hand as your dominant hand, meaning not changing to a 60/40 offside 2-handed grip, but also a 1-handed non-dominant shooting grip, as well?
Kind of like asking a boxer or martial artist how important it might suddenly become to use their non-dominant hand for making critical blows, strikes or punches, maybe?