Overblowing to higher modes lets players reuse the same fingerings to climb registers

Evidence

Once an octave and a fifth above the bot­ tom note has been reached, the flue can be over­ blown to the third mode (an octave and a fifth above the first mode) and the fingering can be started again to ascend higher. The fourth mode is available at the start of the third octave, and so on. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1218