"Trigger Creep" in Single Action Defense Guns

Main Point: If you partially pull a trigger against a sear, and release
the trigger, the sear might not return, and another pull
on the trigger could result in unsafe early detonation.
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I think trigger "creep" is a misuse of the word. Maybe it should
be defined as movement of the trigger during constant pressure
on the trigger. But I will use the common meaning here:
Movement of a trigger after the sear is engaged and to the
point where the sear releases the spring force into either the
hammer/firing-pin, or into a striker-type firing pin, causing detonation.

(A sear is a mechanical catch that holds spring pressure until
the sear slips free, whether the sear contact is metal-to-metal friction,
or some roller bearing crossing a cam high-point in a big gun.)

On a typical single-action trigger, there is "slack" movement of
the trigger until it "grabs"; which is when the sear is engaged.
(striker-fired guns have a "sear", but it engages the striker-pin)
Double-actions use a sear, but in that long trigger travel, the first job
after initial "grab" is cocking the hammer (or drawing the striker)
and pushing a link to engage the sear. The sear then slips free to fire
the gun, often with some element of surprise as to when it will fire.
Trying to guess (or stage) the firing point in a double action is risky.

Once an SA trigger starts sear engagement, you know that you
must be prepared for discharge at any time, since the firing pin,
or striker is almost ready to be launched into the primer.

Some say creep in the SA trigger is a bad feature, but I want creep.
My trigger finger deforms under load, so the direct feedback
is the feeling in my fingertip and in my finger structures.
After reaching the sear grab point, I then want some trigger
sensation as indication of actual sear movement.

When I shoot a rifle at 100 yards when standing ("off-hand"),
I time the sway of the front sight, and I jerk the trigger just before
the desired sight picture is reached. Trying to squeeze a
trigger in that situation means fewer hits on target.

But when using a two-hand grip while standing with a handgun,
I want to squeeze the trigger if I have time. If there is a sensation
of trigger/sear movement past the initial sear engagement, it
helps me to know actually when the gun will fire.
(But if the trigger is a match-grade SA, maybe with a setting lever,
and maybe a pull rated at under 10 ounces, the creep is very small,
since any slip at the sear means the gun will fire.)

There is a downside to trigger creep that is not well known.
When a sear starts to slip (creep), the slip is not normally reversible,
and the sear might be on the verge of release to detonation.
So if you relax your trigger finger after starting into the "creep", but
then decide to resume squeezing, the trigger pull WILL BE SMALLER,
and detonation will be early.
If I have started to squeeze, and I back off, then I might reset the
hammer by backing off on the slide or the hammer. For a striker gun,
I might back off the slide, then bump it closed to get a "fresh trigger".

There are variations on single/double action, and hammer/striker,
which can complicate explanations, but ultimately they operate on
similar principles. Since double-action-only triggers are so awkward,
some of the better guns use a "preset" feature that shortens trigger
travel and trigger pull, while keeping an added safety factor compared
to single action. (something like a half-cocked condition)
.