Double diapering at night

I never understood the point of double diapering with disposables, at least as far as efforts to increase capacity go. Generally the outer diaper doesn't contribute much until the inner one is full, at which point it's just as likely to send liquid out a leg opening as it is to send it through one of the slits you spent all that time making. Unless the diapers are different sizes, anything that makes it past the first leg opening is just as likely to make it past the second one too.