In this mode, both hands play only upper keys on Piano-like keyboards.
All of these keys suit to one another. By that, the playing becomes 100% error-free, such that the right foot can always push the right pedal.
It is useful to play with the left hand often accords and the right hands with a melody or use both hands for a melody of its own, comparable to the Barock fugues.
The octaves with only upper keys have 5 different keys, so the upper keys are pentatonic scales. One can get 5 different scales by using different base keys in playing. These pentatonics scales were used in China and India.
Of course, there exist other pentatonics scales, e.g. for Blues. But these scales loose the easy way of playing, because they mix upper and lower keboard parts. The usage of the upper keys only makes it very simple to play a suitable music on whatever kind of Piano. Restricting to upper keys only is the easiest way for Piano improvisation.