High Low Harmony
tderz: The opening a/o middle game principle Harmony of high & low moves refers usually to moves on the 3rd and 4th lines.
The principle wants to teach that the combination of moves on the 3rd and 4th lines gives you also the combination of stability and territory.
Moves on the 3rd line carry the stability component, while moves on the 4th line add to the prospects for territory.
Moves only on the 4th line get eventually more netto territory by adding the safety of 3rd line moves and vice versa.
tderzGood: _ The high - low combination brings safety and more territory (advice for 10-6k)
 Wrong: All black moves are on the third line and thus low - this is not efficient nor much safer.
Imagine or create similar examples with only moves on the 4-th line.
Dieter: I think this is disputable. The san-ren-sei has all stones on the fourth line, while it is not regarded as disharmony. The 3-4 wave must also typically be a mountain, not a valley. I think it is useful for territory purposes but not as a general statement.
Bill: This is one aspect of the Japanese go concept of balance. As Dieter says, it is questionable, except as regards being too low. Aside from that, I don't know if it has anything to do with efficiency.
Tas: (6k) I guess you want the mountain shape dieter speaks of because you want the 3rd line stones protecting the otherwise open skirts of the 4th line stones' greater amount of teritory. Rigth?
How do you think of this evaluation of early fuseki edge formations.
4-4-4. Open. Not nescesarily bad, but not to be used for teritory directly (san-ren-sei)
3-4-3. Tent. Secure and valuable. Good.
3-3-3. Strong but possibly overconcentrated since it holds fewer points than the above, and the third stone migth not be nescesary for the security. Hence:
3-3. Base. Not for the points but for a secure position in opponents sphere of influence.
Of course the distance between the stones is of great importance too, not just their height.