Do you remember the 2nd game of Habu vs. Itodani? In the opening of this game Itodani lose a tempo exceedingly thus:
You know you will lose a tempo if you exchange same pieces on default squares by yourself. So a normal Bishop-Exchange opening progress like thus:
Black has forced Black to move B-77 to prevent pawn exchange on 8th line. Therefore Black doesn't lose a tempo.
After this position next is a development which you must imagine when you play this opening:
This position is so traditional that have been played for one hundred years. But present masters made a temporal conclusion that Black has a advantage. See comments of this article as cf..
The Kernel Idea
Way back to the game of Itodani. Probably one of what he aimed is a position below:
He will move G52-43 or N-73 here.
Compare this and previous position carefully. White become able to move the rook-side knight for 85 smoothly as the result of withholding P-85 here.
Now White is almost hopeless to attack voluntarily because lost a tempo, but from the start Bishop Exchange is the opening that Black inclines to get a hegemony over first attack due to this symmetrical position. Then, why don't White make a position specializing in counter attack? That's the kernel of sacrificing a tempo.
In fact the winning percentage of White is not so bad in spite of losing a tempo.
In the next article, we look over specific developments after the position and other Black's measures.