It can he a very handy device!!
As mentioned it was probably more for the calvary...but with bike partol, running, jumping, falling, and the crazy hecticness of close in combat it is handy to keep your handgun nearby if it falls out of your hand.
I spent 4 years in Alaska and I found it had other uses on my 1911 Colt! One was for skiing....(cross country), if you slipped while trying to shoot(a snowshow hare and Ptarmigan come immediately into mind), ye old handgun will not disppear into a snow drift. Another cold weather use was to tie a loose knot in the lanyard, and place your hand on the inside of the knot when you are crashing in a sleeping bag or other hostile sleeping arrangement. You hand is not on the gun, but not far from it either! I learned that trick from a Korean War Vet who had ChiComs running around bayoneting sleeping bagged Americans one night. The .45 caliber hole or holes) exiting the sleeping bag makes future nights uncomfortable, but it is better than a 7.62 or bayonet coming in and at least you have other nights to sleep through.
In the Marine's, the lanyard was thought to be silly, until you got out into the field or started doing amphib operations. Ever tried to wade ashore, after jumping off a ramp into a tumultuous ocean with a pistol in your hand? At Mountain Warfare School, the lead climber often only had a pistol(maybe a Mighty Mattel strapped to his back, but it was most certainly hard to access quickly there), and the lanyard meant he still had it with him on arrival at the top.
I have seen training photos of SEALs with coiled lanyard attached to their SIG's. I imagine they use it for the same reason, to keep in attached to their body whilst assaulting oil rigs, comng up through the surf, etc. Your weapon does you little good in 20 fathoms of water.
When it is not attached to the pistol, you can call it a key ring, to dangle your keys over your neck if you do not want anyone knowing what it is really for(courtesy of an experience with a curious NYPD Officer who would not have been thrilled if I told him it was for my Colt LW Commander I had stashed in my bag).
Not a bad idea at all, still have one in my shooting bag, just in case!
DVC,
Jercamp45