When a new WOW patch comes out there are always new systems and currencies. It isn't necessarily a problem to introduce these things as people do like having new stuff to do, and you need to gatekeep your new material to some extent. If you don't, people will stockpile resources before the patch, buy all the new stuff in the first 10 minutes, and then complain that there is nothing to do.
Sometimes, however, they miss the mark badly. In the latest 9.2 patch a new currency was introduced that is called Cosmix Flux. CF is acquired from everything - dungeon runs, raids, treasures, rare monsters, pvp, all these things give it to you. It isn't rooted in lore anywhere either, it just rains from the sky for no reason. I like stuff that is rooted in the world - silverleaf is an herb found in a few starting zones, has a particular look, and is used for particular things. I like that. CF, on the other hand, comes from everywhere and has no lore or meaning. Given that it totally fails from an immersion standpoint, it needs to be excellent on some other front.
It is not. The main issue is that there isn't much you can do with it. In the first week of the new patch I determined that I would need at most 12,000 CF for the near future, and that might rise to as high as 20,000 under some odd circumstances. By the time I had calculated this I had already gathered 10,000 CF without making any attempt to hunt for it. At the current moment I have 30,000 CF sitting around and there is literally nothing I can do with it. I can't specifically gather it and it has no use - why does it exist at all?
If a new currency is rare and is useful for something specific that can be a good thing. People enjoy hunting for ways to build new stuff or acquire cool toys. A generic currency that is worthless is a total waste though - it irritates veterans as it is just one more damn thing I need to scroll past, and new players get overwhelmed by new systems. For a system to be worth learning it has to have redeeming value, and this one has none.
Last week I concluded that Blizzard would end up using CF to patch up mistakes they made in this new patch. Anything that was too hard to get and which players complained about would simply be put on a vendor with a cost of CF so that people would be able to get tons of it (but not infinite amounts).
Lo and behold Blizzard just announced that two old currencies which people were complaining about got added to a vendor for a cost of 3,000 CF. It feels extremely kludgy and immersion breaking to me. They screwed up the values badly, added a pointless currency and system creep, and now are trying to fix other issues they created (which could have been neatly solved in other ways, I might add) using their screwup.
One thing about systems in games is that every system has cognitive overhead. To justify this overhead you absolutely must have a good reason that the system exists. Just adding in stuff to be adding in stuff is a terrible choice, and one they should stop doing. My currencies tab is already bursting with one hundred old, pointless currencies, and we don't need to be adding a few more every couple months.
A game is complete when there is nothing left you can trim out, not when you have added every damn thing you can think of.