Gdddk

Many traits and (some feats, if my memory is right) have this rule written in them. For example:

Trap Finder

Benefit(s): You gain a +1 trait bonus on Disable Device checks, and that skill is always a class skill for you. In addition, you can use Disable Device to disarm magic traps, like a rogue.

Emphasis mine.

I'm unsure about the "always" word. Back in the days of 3.5, if you were spending points on cross-class skills, you got ½ of a rank per skill point spent. Thus, abilities that made a skill an always class skill was very usable for characters wanting to multiclass or take PrC.

In Pathfinder, only effect of skill being a class skill is +3 bonus. Thus, there is no sense to say that skill is always a class skill, right? It either is or is not?

Is there any meaning, rules-wise, to this always word in such rules? Am I forgetting something that makes it meaningful? Or is it but a reminiscent of D&D 3.5 era?

That word is only there because of certain rules were changed between 3.5 and Pathfinder, such as how class skills work and how multiclassing works, and they needed to clarify that the skill is a class skill regardless of your class(es). It has no actual effect, if a skill is a class skill, it is a class skill regardless of your classes and other mechanics, and there are no mechanics that make it not be a class skill for you.

However, there are archetypes that change your class skills for that class, and saying that this always count as a class skill should bypass a possible removal from an archetype. There are many examples of this, but to name one, the Urban Bloodrager removes some skills from their list of class skills:

Class Skills: An urban bloodrager adds Diplomacy (Cha), Knowledge (local) (Int), Linguistics (Int), and Profession (Wis) as class skills, and removes Handle Animal (Cha), Knowledge (nature) (Int), and Survival (Wis).