So that’s a great, great aspect of allies, for those of us who can’t get enough of theoryhammer/listhammer. 
But
 I’m not here to talk about why *I* like allies, but instead why allies 
are good for The Hobby, and bring it closer to the vision that I think 
Games Workshop has always desired, without ruining it for those of us 
that actually enjoy going to tournaments (competitive, well-designed 
tournaments).
So
 allies are good for competitive players, I will argue. I believe they 
are a poor-man’s fix to codex creep and balance issues, with a nod to 
fluff thrown in. Armies can shore up weaknesses in their own unit 
selection by borrowing from other’s repertoire’s. Tau seem to me to be 
the stand-out winners here. With the ability to work with anyone, and 
firepower units but a paucity of good troops and screening, they have 
gained a LOT. Personally, I would be looking at Orks if I was playing 
Tau as a kick-ass supplement, but that’s just me. 
But
 I also indicated that allies are good for less competitive gamers, and 
help to realize the vision for The Hobby that Games Workshop has always had (I think).
When
 you are a competitive player, you build armies. You don’t collect 
armies, you build them. There may be some exceptions to this rule, but I
 think they are few and far between. You start with theory, you come up 
with a concept, you probably proxy and playtest, you discuss with fellow
 gamers, then you buy the units you need and, if you are also a painter,
 you build and paint them to a tournament standard. You may have some 
flexibility within that army. Maybe you have some Wolf Scouts and Lone 
Wolves and swap them out interchangeably. But probably for the most part
 your army is your army. 
When
 we talk about building an army, we are talking hundreds of dollars. We 
are talking 2000 points. We are talking hours and hours of invested 
time. 
Games Workshop wants you to collect units, not armies.
I
 distinctly remember reading old White Dwarfs, and I’m sure it hasn’t 
changed too much. The basic premise is: Buy a unit. Build the unit. 
Paint the unit. Throw it into your army and try it out. 
For
 casual gamers and collectors, this works quite well I imagine. Say you 
are an Ultramarine player. The new honour guard models come out. Oh 
neat, I think I’m going to go buy that box. You buy the models, build 
them, paint them. For your next game, in they go! 
Bully for them. 
But this tends to lead to mono-army-itis. 10000 points of boyz in blue. 
Allies
 allow for a blending of these two approaches, opening the door for both
 casual and competitive gamers to become collectors. 
Now,
 if you find Necrons or Dark Eldar interesting, but aren’t sure you want
 to dump 600-700 bucks into an army, you can still play them. Buy your 
HQ, and a unit of troops, and you are off to the races. Add a unit of 
Fast Attack, and into your army they go. 
This
 will also alleviate, to some extent, the “Lots O’ Marines” epidemic. I 
think most people start playing the latest Marine codex because they 
already have a bunch of the models they need, and it gives them a chance
 to try something new. If you already have 12 Rhino hulls you can use 
them in any Marine army you want. There is relatively little incentive 
to try a Xenos army, because Xenos armies require a totally new 
investment in a complete, new army. 
Now,
 if a Xenos codex releases, you don’t have to buy a full 2000 point 
army. Again, HQ and a Troop, and you are ready to integrate into your 
existing forces. Tau are positioned to sell like hotcakes to… EVERYBODY once their new codex drops.
 Anyone can use them, and you don’t have to dump the better portion of a
 grand to do it. 
I
 will say, army paint judging may have to flex a bit. I can imagine it 
will be hard to have a visually “cohesive” force if you are running 
Ultramarines and Necrons together… 
At the end of the day, I think this is a really good thing for everyone, including Games Workshops. They will more easily sell models, we will more easily try out different things... it's a win win.  
 
