tips about price manage, Price tab and price impact field

[ballashop]

Hi,
I have a curiosity about the assignment of prices and how to manage them, I would like your opinion:
I have 3 ways to manage item prices in our shop:

1) the product has no variations and the price is unique.
2) the product has variants but the price of these are all the same (e.g. shoes size).
3) the product has variants and each of them have a different price.

So...

1) I add the price only in the "Prices" tab

2) I add the price only in the "Prices" tab and the variants have no price impact set

3) I add the price only in the "Impact of price" variants and leave the field at 0 in the "Prices" tab because there is no base cost.

For example 1 and 2 everything is clear, for example 3 I am not sure I am doing well.

I don't manage the cost or vendor price, so I've never used this field.
Prestashop is used only as a sale with the list prices without VAT.

Version 1.6.1.24

We do not use third party modules to manage price catalog.

Thanks for any tips