For those who always think Diagonal Lashing is used as long as two poles are not intersecting at 90 degrees, this article below informs us about the correct usage of using this form of lashing:
THE DIAGONAL LASHING
Diagonal lashing is used to bind poles together that cross each other but do not touch when their ends are lashed in place in a structure.
The diagonal lashing gets its name from the fact that the wrapping turns cross the poles diagonally. The diagonal lashing can be used to bind poles that cross each other from 90 degrees to 45 degrees.
The diagonal lashing makes use of the timber hitch to pull poles together that are not touching each other. The timber hitch allows the poles to be drawn together without changing the relative positions of the poles. [NOTE] If a square lashing were used to bind poles that do not touch, the beginning clove hitch would pull the cross pole toward the clove hitch causing unnecessary bowing of the cross pole and could also produce a force that would act along the length of the pole to which the clove hitch is tied. These additional force, if strong enough, can place unnecessary strain on other lashing within the structure causing the structure to twist and fail.
In simple words, the diagonal lashing is used to pull two poles together which has a gap in between them, for e.g. the ‘X’ part of a trestle when you make your chariot. On the other hand, the square lashing can be used to bind poles that cross each other from 45 to 90 degrees as long as it doesn’t fulfill the condition stated above.