When does item AC / Dex matter?

[Archaeik]

I suppose I mean magic items specifically

Magic Item Descriptions wrote:

General descriptions include notes on activation, random generation, and other material. The AC, hardness, hit points, and break DC are given for typical examples of some magic items. The AC assumes that the item is unattended and includes a –5 penalty for the item's effective Dexterity of 0. If a creature holds the item, use the creature's Dexterity modifier in place of the –5 penalty.

I'm under the impression that the only time item AC matters is when it's unattended.

If an item is attended, attacks against it use the creature's CMD, do they not? (The lone outlier here may be Ioun Stones, but to my knowledge, it's never been resolved whether that language is only a holdover from 3.5, having no PFRPG function)

So what is the purpose of adjusting the held item's Dex modifier?
AFAICT, non-intelligent items have stats of (-,-,-,-,-,-) and only replace their effective Dex 10 with Dex 0 for the purpose of figuring AC because it is the rule.

Does it affect a held item's Reflex save or is the base save of 2 + 1/2 CL fixed? (instead of shorthand for "2 + 1/2 CL + Con/Dex/Wis(normally 0)")

Related from another thread
If a creature is denied its dexterity bonus, is a held item also denied its bonus?
RAW is a little sketchy, and I'd say 'not expressly'.
RAI is potentially 'yes by extension', but I have nothing to support that.

[Nefreet]

I'd say that the vast majority of the time you're going to be targeting the wielder's CMD (vs Sunder, Steal, whatever).

I know there's maybe one or two references to item AC instead, and in those corner case scenarios you would use the AC of the item.

I don't think there's a problem in the rules, I think that item AC is used so infrequently that those rules seem incorrect.