Are there any drawbacks to using Unity's primitive mesh types?

Questions & Answers
1

i.e the standard “Cube”/“Sphere”/“Cylinder” meshes that come with Unity.

I’m doing a very basic game to just get my feet wet and the standard meshes seem sufficient for now when used with custom textures.

However is there any major limitation to using these? eg: lightmapping/auto-generated lightmap UV issues/etc. I understand custom texture UV mapping will not be possible but that sounds acceptable for my limited usecases.

2

There are no limitations whatsoever to using the standard built-in meshes in Unity, and you’re free to change their UVs to whatever you want. To see how, consider this script (C#):

private void Foo()
{
    GameObject stdSphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);

    Mesh sphereMesh = stdSphere.GetComponent<MeshFilter>().mesh;

    Vector2[] yourOwnUVs = new Vector2[sphereMesh.uv.Length];

    for (int i = 0; i < yourOwnUVs.Length; i++)
    {
        yourOwnUVs *= // ... Setup whatever you want your own UVs to be, then assign them back after this loop*

}
sphereMesh.uv = yourOwnUVs;
}