I'm afraid I still don't understand what you mean by "non-associated" class levels.
If you add class levels to a monster, you need to consider the role of the monster first. If you give it levels that mesh nicely with the monster's abilities and role, its CR goes up by one for every class level it gains. Many giants are heavy melee bruisers, so giving them levels in fighter or barbarian reinforces that role, thus giving the giant in question +1 CR per fighter or barbarian level. These would be considered associated class levels.
Now let's take another class and add it to your stereotypical hill giant, like the druid class. Hill giants do live out in the wild, but they aren't the wisest of critters. A druid level won't improve the monster's combat ability much on its own: no BAB, no bonus feat, no rage, etc. Two levels gives it a bit more staying power. Sure, it got a bump to saves at 1 level, plus 1st level spells, but the hill giant really isn't set up for the druidic path when you look at its stats. Druid levels would be considered non-associated class levels.
Stuff.
Ah, okay. I'm following you now. Unfortunately I've never really experimented with that and so don't have much to contribute. Sorry.
Like, for Giants the associated levels would be the martial classes, like fighter, ranger, barbarian. The non-associated would be the spell casting things, like sorcerer. One level of barbarian would add 1 to the CR but 2 levels of Sorcerer would add 1 to the CR.
Maybe Pathfinder doesn't have this anymore.
It's still in the Bestiary, as an option for advancing monsters. They just didn't call them non-associated class levels anymore. Description's there though.
there is a change from 3.5 though... in 3.5 non-associated classes provided a cr increase on a 2 levels to 1 cr basis until the total levels equaled the creatures base HD after which switched to 1:1, in pathfinder it is 2:1 until the total level reach the creatures base CR after which it is 1:1
for example adding wizard levels to a stone giant (using the stone giant HD of 12 and CR of 8 from the bestiary for both examples because they are just examples)
Using the 3.5 method every other level of wizard you add to the stone giant increases its CR by 1 until you reach 12th level, after that each level increases the CR by 1 (So adding 4 wizard levels makes it a CR 10 creature, adding 8 levels makes it cr 12, add 12 levels makes it a cr 14, adding 14 levels makes it cr 18 and so forth)
Using the Pathfinder every other wizard level increases the giants CR by 1 until you reach 8th level, after that it increases on a 1 for 1 basis (adding 4 level makes a cr 10 giant, adding 8 levels makes a cr 12 monster, adding 12 levels makes a cr 16, adding 14 levels makes it cr 20, and so forth).