Helical net diagrams are used to represent the arrangement of side chains in α-helical regions of protein. Also you can say a separate representation that involves a hypothetical razor cut lengthwise along the helix axis, followed by unpeeling the surface of the helix. This result in a plot of distance along the helix versus distance around the helix called a Helical Net. The helical net does emphasize the distance along the helix, which is ignored in the helical wheel. Compare the two representations, and note the relative positions of different residues. In the helical wheel, residues 1 and 8 are quite close together; the helical net shows that these residues exhibit a 10.5 Å vertical separation (although they are still present on the same side of the helix).
Both helical wheel and helical net analysis types are useful for analyzing the helix for patterns in residue properties around the circumference of the helix. The helical wheel is somewhat easier to interpret, but leaves out the sometimes-crucial distance information.
So we can conclude that, a common reason for using a helical wheel or helical net diagram is to look for helical regions that exist at protein surfaces. The interior of a protein is typically non-polar, while the surrounding solvent is polar. A helix that has its axis along the border of this region would be expected to have a corresponding, amphipathic, distribution of polar and non-polar residues. (Amphipathic, meaning “hating both” refers to the presence of both polar and non-polar groups in the helix.)