Cutting the Keima
Cutting the keima without support will usually strengthen the opponent.
After the cut with and , White has extended from a crosscut and sente which is very advantageous for him. Next, may capture the cutting stone in a ladder
So, cutting a keima is only advised when the attacker has support from other stones.
A genuine cut
When is present, the cut becomes more severe. If the ladder at a works for Black, is a genuine cut.
Striking at the waist of the keima is usually the correct way to cut. We refer to that page to understand why that is so.
If on top of , there is also a black stone , the same sequence results in a very severe cut.
When cutting the keima is strategically important, this diagonal cut (kosumigiri) is sometimes used mainly if a) the ladder is bad for Black, or b) Black has another stone at x, avoiding an empty triangle. This gives White more forcing move possibilities ( a to d ) than the genuine cut above.
Comparing to the one space jump
If we compare the genuine cut above with this one, where Black tries to cut a one space jump, we can see that White is reinforced and weakened, even if Black can next continue to cut at a. We can say Black has effectively cut himself here rather than White.
OC, that is ridiculous, since there was no Black to get cut to start with.
These diagrams show why, in hostile environment, the more stable one space jump is preferable for defending, whereas a keima is often more appropriate for attacking purposes in friendly environment.
Would that things were so simple!