What does melted butter do in a swiss roll recipe? I'm planning on making a Swiss roll. This is a sponge cake, baked in your baking sheet (so it's thin) and you roll it up, mostly with a filling.

While looking for a recipe, some recipes say to use the same recipe as for a regular sponge cake, but add some melted butter. Other recipes don't mention melted butter and stick to eggs, sugar and flour.
I'm wondering what the function of the butter is in a Swiss roll. Does it help with rolling? Or is it just taste? Can I omit it?

(I would omit it if it's just the taste. My filling will be butter cream.)
I have never added butter to sponge sheets when making swiss rolls, jelly rolls, or anything similar in the past. It's just straight up bread flour, sugar, and eggs.

I can only think of three possible reasons why butter might be added:


To improve the flavour;
To keep the sheets moist and help prevent overbaking, as any fat would be used in cake batter; however, this is generally not a major concern in cake rolls; or
To help prevent it from sticking to the sheet (don't bother; if you have this problem, use a silicone mat).


Reasons #2 and #3 aren't very convincing to me, so I would only bother adding butter if you prefer the taste of swiss rolls with butter added.

I don't think butter would help with rolling at all, in fact it might make rolling more difficult on account of making the sheets more crumbly and less able to hold together under pressure.