Expand or Invade?
Build or destroy? Expand one's moyo, or rather invade the opponent's moyo?
It is hard to give meaningful guidelines about when to do what. At least in the Japan, learning by example is a big thing - so here I am going to give an example from one of my official insei games.
Black to play
This game in Dia 1 is still early, so there are many options for black. Think of your top 2-3 options, each with pros and cons and with a few follow-up moves.
In Dia 2 I simplified the problem by providing 3 options for Black's next move. Which one do you like best?
A move around 1 in Dia 3 is an attempt for black to expand his upper side territory. Black is ready to help white build territory on the right side, since his upper side moyo is much larger.
The truth is that Black's upper side moyo is indeed very large - in fact it is too large to make it into territory. The upper side is still open, and white has an excellent reducing move at A. For this reason, to give white free territory on the right side in exchange for expanding such a moyo is not a good idea.
Since black cannot construct a promising moyo on the upper side, he should better invade White's.
Another nice move for black is to extend on the lower side - not only does black put some pressure on the white group in the lower left, but he is also preventing white from extending in that area and Black's stones on the lower side into a weak group.
- To judge a sequence where both you and opponent build, here is one good rule of thumb: ask yourself if what you build is enough to win - if so, go for it. If not, then invade or reduce the opponent's moyo instead of building.
- Don't invest into building a moyo that's open in too many places - better go for a "money in the pocket" move that builds or reduces firm territory.