"Phasing", the techique to change the environment and NPC's via quest completion is touted as "solving the problem" of quests never having any lasting impact.  Phasing was implemented a tiny bit in BC, some in WOLTK, and after mostly favorable reception, extensively in Cata.

But what does "phasing" really give us?

Pros

NPC's and environment changes upon quest completion

Advances "the story"

Cons

NPC's and environment changes JUST FOR YOU upon quest completion

NPC's and environment changes feel canned or scripted

Are we in a "story" or a "world"?

Many players cannot see one another if they are out of sync in their quests

World feels disjointed and empty

Familiarity with zones and NPC's lessened since they "change" through phasing

Considering the "cons", extensive as they are", are the "pros" really enough to justify extensive use of phasing?  I, for one, question the immersion that phasing proposes to enhance.  Changing something just for myself, while it does not change for someone standing next to me, is a hit upon my immersion. 

I think "phasing" is a cheap development gimmick that will pass or fall into limited use.

Thoughts?

I don't personally agree with some of your cons, but I think that's because they're your opinion (which is fine):

NPC's and environment changes JUST FOR YOU upon quest completion

I don't see how this is a con?

NPC's and environment changes feel canned or scripted

Well, it is a game, developed by people; I personally love a good story. Do movies feel canned or scripted? Plays? I don't feel this is a con.

Are we in a "story" or a "world"?

I see your point; I guess I would rather be in a story, personally.

Many players cannot see one another if they are out of sync in their quests

I agree with this, and this is a concern. I usually duo with my fiance and this can happen, forcing us to only play together and not get far ahead/behind.

World feels disjointed and empty

I don't personally get this feeling, at least not from phasing. What I always found jarring was the size of the world (deep jungle just a few minutes away from wheat fields, etc.).

Familiarity with zones and NPC's lessened since they "change" through phasing

I see your point; but it seems to me (and I didn't play everything there is to play in the game) that most NPCs you will be interacting with on a more regular basis (like merchants, token vendors, etc. as opposed to quest NPCs) pretty much stayed in the same place or area.

Mainly, I just wish they didn't have so many "bombing run" quests. The first one was like "cool!" the second, "whoa, again?" and after the 20th or so..."oh, this again..."

Cons

NPC's and environment changes JUST FOR YOU upon quest completion

Of course they change just for you. That's what phasing is supposed to do. You can't change the world for all players permanently. Not in an MMO game. I am pretty sure you know why. Phasing tries to "fix" this problem.

NPC's and environment changes feel canned or scripted

I find all games to be scripted. They are games. Of course they are scripted.

Are we in a "story" or a "world"?

It really depends on your definition. How do you define "world"? I personally play RPGs for the stories they tell.

Many players cannot see one another if they are out of sync in their quests

This definitely sucks. But it doesn't have to be this way. Blizzard are trying a new approach to phasing in 4.2 where you can see everybody in spite of the stage they are on.

World feels disjointed and empty

Disjointed, maybe. But empty? An empty world is one which lacks any story/lore.

Familiarity with zones and NPC's lessened since they "change" through phasing

Should we have static NPCs and environment because of this?

i'd say no it isn't worth it at all for wow. it could be useful in a story-based game, though. maybe gw2 or swtor as they supposedly have story in them. in wow all it really does it make the area you're grinding in seem more empty.

I also agree that phasing hurts wow more than helps it

under 85, if you do quests in the outdoor world, you rarely see any players outside of cities

- players are using the dungeon finder

- pvp

- phased in questing