One cup of sugar or two?

I have been doing diy co2 for quite some time using 2 cups of sugar when I ran across an article stating 1 cup of sugar is better, since there is really no need for the extra cup. Does anyone know if this is true? I tried just using 1 cup of sugar the last mixture and it seems to produce just as long, but I am unsure of the consistency of the mixture over time. Thanks.