Granulated or caster sugar?

[milkmoustache]

Are there any recipes where substituting one for the other would really make a difference?

Sponge cakes need caster sugar. If granulated is used the cake is rather ... granular.

anything where texture is an issue.

if you only have granulated you can just whizz it in a blender to refine it down a little
( ihave had to do that when short of caster for cake making)

Yes Caster sugar is just for lightness really.

The onlly thing that I learnt the other night (on here) is that icing sugar is not pure sugar and has cornflour and stuff added so you can't really switch between icing and other sugars.

I only buy caster sugar now, as it's just easier.

My children always want to cook when I dont have caster sugar in!
They have never complained at the results - nor has their father! I think it depends on how perfect you want the results to be.

If you are using American (ie volumetric) recipes, you really need to use caster sugar.