Here you can change the weights of ingredients with more options compared to the options in the main dialog.
If you check this checkbox that ingredient will not change if you modify any of the New weight cells. So, this locks the weight of the ingredient. The locked checkbox is not used when changing in the Limit weight column.
Changing these cells will scale all other ingredients, except if the locked checkbox is checked, to keep the same total weight.
Changing in these cells will scale all other ingredients so that all the properties and data of the recipe is maintained. This is useful if you for example have a smaller amount of one ingredient than the recipe calls for. Say you make strawberry ice cream and need 300g of strawberries but you only have 350g, then you can use this method.
New weight edit
Changes the total weight by scaling all the ingredients except if the locked checkbox is checked.