Here is an example with different collisions in the same area: Whiterun's stairs

The collision shape determines how smoothly you move up the ramp/stairs.
True high poly stair collision has a bumpy, 'snap up/down' effect on the character, as there is no smoothing system to prevent it.
This is inconsistently used across the game ~50% of the time, with low poly slope collision otherwise.

Other places with this: Imperial tower staircases, scaffolding stairs, High Hrothgar, etc.

The stair flag/material, if applied onto the collision, disables Foot IK while moving.
Foot IK snaps the character's feet onto the surface of collision, allowing for individual foot heights with knees bent.
In the base game, since the flag is present on most stair objects, it results in floating feet while moving.
This can be an issue if if the flag is missing on slopes, as the feet then point at an angle up/down despite walking on a 'flat' surface.

Personally, I prefer slopes and the stair flag enabled. This prevents the angled feet and has smooth movement.
CLAMBER then compensates for no IK by introducing the lowered feet in the animation itself.
There's no consequence to this if the stair flag is disabled! It just looks a bit different.
This is pretty common in-game, thankfully!


Extreme Accuracy Mode

'Extreme Accuracy' turns off smoothing for angle checks.
This means that animations will instantly start and stop depending on stairs, navmeshing, collision, etc.
This can fix animation lingering and slow trigger speed, at the cost of jittering and multiple footstep sounds.

The Extreme Accuracy Preset is very, very dependent on navmeshing.
Areas with no navmeshing will have angle checks rely entirely on the collision of the meshes you walk on.

...

If you've looked in OAR, you may have noticed that the Smoothing factor looks like 1.0 regardless of the preset.
In the default presets, they're rounded up to 1.0 in the menu- the actual value is 0.9999... etc.
This makes a massive difference!

(Advanced)
I want to play around with angle detection, what should I tweak in OAR?

Spoiler:  

Show

Under the MovementSurfaceAngle condition in the presets, the options are self-explanatory:

The value is the angle that is checked, from 0 - 1.
Degrees instead of 0 - 1 is there if you want it, but beta OAR didn't have it until later so I didn't use it.
This value was tweaked and tested for a long time alongside smoothing before release.

Use Navmesh should always be on.
In the very first spoiler under the gifs at the top of the description, I explain high-poly collision vs. low-poly collision.
Imagine you're on high-poly collision stairs: The surface 'angle' is constantly jumping from 0 to 90 degrees, over and over.
This would cause the animation to suddenly start and stop multiple times within the fraction of a second.
Using the navmesh instead of the collision typically remedies this, as navmeshes are always simpler, like a slope.

The smoothing factor changes the angle detection speed.
Rapid changes in angle are 'softened,' which helps prevent some jitters & rapid footstep sounds off navmeshing.
This comes at the cost of responsiveness, however.
The values in the default preset are 0.9999~ in the config.json, just rounded up to 1.0 visually in the menu.
(0 = high smoothing, 1 = no smoothing.)
The 'Extreme Accuracy' presets have smoothing disabled- actually set to 1.0.