Nil purpose for recipe/technology difficulties?

[Perlin]

Hello,

If I'm correct (from what i read on the Wiki), if I set "nil" on the normal difficulty, the recipe will use the properties of the expensive difficulty. What is the purpose of doing that? From what I understand, these two definitions are the same :

Code: Select all

  {
    type = "recipe",
    name = "iron-gear-wheel",
    normal = nil,
    expensive =
    {
      ingredients = {{"iron-plate", 4}},
      result = "iron-gear-wheel"
    }
  },

and

Code: Select all

  {
    type = "recipe",
    name = "iron-gear-wheel",
    ingredients = {{"iron-plate", 4}},
    result = "iron-gear-wheel"
  },

Thank you

[Honktown]

I thought the reason was so the recipe is disabled on normal difficulty. If I'm wrong I'm wrong.

There may have been a niche reason, because I thought there were two ways to specify recipes? Like how result got expanded into results?