Series and parallel principle for weak groups
There is a range of possible weak group strategies, such as these:
- Never make weak groups
- Settle any weak group as quickly as possible
- Aim to have just one weak group in the middle game
- Make several weak groups that cannot be jointly attacked
- Make several weak groups to create confusion
- Make weak groups and then sacrifice some of them
- Make the maximum number of weak groups, to make the game as difficult as possible.
Most of these ideas (1, 2, 5, 7) can be criticised as bad advice. Probably they apply in particular positions, but they are wrong from the point of view of general principles. For example if you are well ahead in the game, #2 is good advice, while if you are a long way behind #7 is perhaps appropriate, if only as a way to set up a resignation.
Even #6 is debatable, from the point of view of aji keshi versus light play. It depends perhaps on the precise handling: invading and then sacrificing the invading group for something else may be a good idea, but only if the trade-off is interesting. Otherwise some aji has been given up and one's options are narrowed down.
Therefore it is hard to give strategic ideas at the general level. One serious principle is to modify #3 to the idea that one wants a single weak group at any one time, but the plan can be to make a series of weak groups that invade or reduce the opponent's frameworks.
The slogan is parallel bad, series good. Don't make weak groups in parallel (simultaneously), but do plan invasions while thinking about the following invasion or reduction in the series.