The reason for the cut away trigger guard was to give unimpeded access to the trigger for fast use.
This was John Fitzgerald's idea of a "gunfighter" modification done in an attempt to speed up using the gun.
For most people getting to the trigger wasn't a problem, but John Fitzgerald was a HUGE man with hands like catchers mitts and fingers like bananas.
Even with his favorite Colt New Service models he still had trouble so he cut the entire front of the trigger guard away.
He carried one or two of these altered Colt New Service models in his hip pockets, which he had lined with stiff, waxed canvas.
In his hand a Colt New Service looked like a Detective Special in an ordinary persons hand.
A number of early gunmen often carried guns in their hip pockets and often had the pockets lined with waxed canvas, Wyatt Earp among them.
Famed Border Patrolman Bill Jordan also had huge hands and instead of cutting the entire front of the trigger guard away, he cut a half moon clearance cut out of the right side of the trigger guard, leaving enough to prevent the guard from bending or risking an accidental discharge if the trigger got caught like the Fitz Special could.
The Fitz Special was one of those good ideas that lacked in the real world. The trigger guard could get bent, jamming the trigger, and it was way too easy to fire the gun by accident when holstering it or pushing it into the waist band or pocket.
It was just riskier then any benefit was worth.