One-point jump (ikken tobi in Japanese'') is often used to connect groups of stones.
It is not completely secure, since it can often be cut; but in general, the attacker will also end with two cut-apart groups and will find life difficult: cutting the one-point jump.
The one-point jump is often the correct move for defence and is very often applied in running fights. A proverb says that ikken tobi is never wrong.