Hane-descend

Old Joseki  

and is a typical hane-descend to the second line. (White may play at leading to a complex fight - see 3-4 point low approach, two space high pincer, kosumi tsuke)

Example 2:

Straight J  

Hane-descend to the first line is often used in life and death situations to maximize eyespace. For example, is the only possible way to make ko for life - at a is insufficient. See J group for details.

Example 3:

endgame  

and is a hane-descend to the first line in the endgame. Black needs to connect at a later. Though this gives the opponent more ko threats, they are usually not important in the endgame.

comparison  

If Black connects instead of the descent, White has a chance to reduce Black's territory by 1 point via a ko fight.