Query regards Sponge Cake

Hello members, I am looking forward to bake a sugarless sponge cake for the first time. I need to know the role of sugar here, if I remove the sugar and then proceed as usual, what will be the difference? Somewhere i read sugar helps to hold the egg white fluff so one gets a better soft texture.

Also one more query, many recipes I have seen in sponge cake people do not use baking powder, since the egg white have been fluffed properly, the role of baking powder minimizes I guess hence can be avoided, am I thinking right?? Also because after we put the batter in the preheated oven, I do not see significant oven spring so may be baking powder is not beneficial?? Please correct.