"When I am White I win because I am White, when I am Black I win because I am Bogoljubow." - Efim Bogoljubow.

I'm still thinking about this, so bear with me, and comments invited...

I pounced on Nunn's Chess Openings when it came out, and found some things that I found puzzling.  Openings like the Dutch Stonewall, which I had always thought of as being fundamentally flawed, were being shown as equal, while the Classical Dutch - which I thought was a superior approach - was coming out as +=.

Firstly, why did I think that the Dutch Stonewall was so flawed?  Earlier in my life, I had devoured the Euwe/Kramer books on The Middle Game.  Not unlike 1066 and all that, I learned lots of Important Ideas like Isolated Queen's Pawns and Bad Bishops which were worth writing down in Capital Letters.  If you played the Dutch Stonewall as Black, you had a Bad Bishop and White could start in with a Queen's Side Attack, perhaps even a Minority Attack.  I also learned that if you had only one Bishop, you placed your pawns on the Opposite Colour to your Bishop, leaving its lines of action free. 

So, for example, in the Bogo-Indian, after ...Bb4 and an exchange of dark-squared Bishops, a very logical plan for Black was ...d6 and ...e5, challenging in the centre on the dark squares, and releasing the light-squared Bishop on c8.

Imagine my confusion, when reading Nunn et al., to see that the lines of the Bogo-Indian with ...d6 and ...e5 were generally given as +=, while Black seemed to have better chances of equality with Ulf Andersson's  favourite ...d7-d5, leaving the central pawns on light squares, and obstructing our remaining Bishop.

I'm still thinking about this, but needing some sort of explanation, I reached for these ideas:

a. After ...e6-e5 and d4-d5, how strong is Black's claim to have a Good Bishop?  After all, where can it go?  In the game Pedersen-Shkapenko (GM 2007), we reached this position:

We can see that the Bishop on each side can only go backwards!  The fact that Black's Bishop has a choice of retreats does not seem very relevant to me!  This position can be better understood by thinking about the rest of the pieces, and it seems as though White's space and centralised Knights offer a plus.  The Knight on d3 looks especially well-placed, supporting pawn breaks on both sides of the board.  White can look forward to arranging c5 at leisure.

b. When you play ...d7-d5.  White has a pawn on c4.  After an exchange of pawns, new career prospects appear for the Bc8.  White can stop this only by c4-c5, but then Black has ideas of ...b6 and/or ...e5, both of which attack White's pawns and release the Bc8. 

c. In Queen's Pawn Openings, after ...e6-e5 and d4-d5, White has a natural plan of pushing forward on the Queen's-side, with moves like b4 and c5.  ...d7-d5 concedes less space on the Queen's-side, and importantly, doesn't hand White a simple plan of campaign.  That feels quite a good explanation to me.

d. One last consideration: Black often has a small lead in development, which is used better by playing ...d5 quickly than ...d6 and ...e5 slowly.  In the Nimzo-Indian, White is often embarrassed by Black's quick ...d7-d5 break, even though in the long run White will want to open up the position for the two Bishops.  Black can castle and get in ...d5 before White has touched any of the King's-side pieces.  In the Bogo-Indian, White might not have the Bishop pair, but the time factor could still be relevant.  I'm not sure how important this idea is in every line; we'd probably need to look at some variations.

Overlapping explanations might help us to understand the Dutch Stonewall.  There Black has some claim to be the side with more space, and White's allegedly Good Bishop on g2 seems to have just as poor career prospects as Black's on c8.  So again, simply interpreting the position through the most obvious difference - the effect of the pawn structure on one pair of pieces - was Too Simple.  That is very definitely a Bad Thing.

"The Euwe books are very good for beginners.  But after a while I began to think that everything Euwe wrote was a lie!" -- Bent Larsen.

To be honest, if the Bogo-Indian ever turns up on my board, I'll still be strongly drawn to ...d6 and ...e5.  As much as it hands White a plan, it also gives a position where I think I also know what I'm supposed to be doing.  After ...d5, even if the position is more equal, I'd feel more at a loss as to what to do!