Another example: Invisible Woman
She has Force Blast D10. But an attack narrated to multipower it with Godlike Durability D12, a hammer-and-anvil attack where the force blast slams the target into a force wall, would get D10+D8. Or multipower force blast with Invisibility D12, something where she sneaks around and blasts from an unexpected direction, and get D10+D8.
A further benefit: Sue doesn't have a Combat specialty, but a multipower might allow her to add in a different specialty, that a straight force blast wouldn't justify. For example, a "sneak around and blast" attack might add her Covert Expert D8, since Covert includes sneaking skills.