Smoothing groups and custom vertex normals

Smoothing groups

Maya and Blender use a simplified method of model shading - Hard/soft edgе.

it needs to be created with hard and soft edges with the right degree of angle between two adjacent polygons, thereby affecting how the model is visually rendered.

The image below shows the same cube with minor differences:

1. Cube has all soft edges, with support ribs (support loop) like a subdivision model.

2. Cube has a correctly distributed Hard soft edge

3. All the edges are set to soft edge

4. All ribs are set to Hard edge

If the model will be baked with Highpoly, pay attention to the anti-aliasing groups. Otherwise baked Normal maps will have noticeable artifacts.

Custom vertex normal

Custom vertex normal is often used on chipped walls, on creating a fake roundness of an object, and on fitting the desired bevel display.

Custom vertex paint is often used when it comes to Handpaint styling (World of warcraft, genshin impact, etc.).