Each has no effect when there is no turbulence. Octaves value controls the number of steps of turbulence that are computed. Legal values range from 1 to 10. Float values are truncated to integer. Smaller numbers of octaves give a gentler, wavy turbulence and computes faster.
Higher octaves create more jagged or fuzzy turbulence and takes longer to compute.
Section 7.6.8.6 Lambda parameter controls how statistically different the random move of an octave is compared to its previous octave. The default value is 2.0 which is quite random. Values close to lambda 1.0 will straighten out the randomness of the path in the diagram above. The zig-zag steps in the calculation are in nearly the same direction. Higher values can look more swirly under some circumstances.