How did Macbeth stand to benefit from the "bloody business"?

Macbeth refers to the planned murder of King Duncan as "bloody business" when he delivers the soliloquy in which he hallucinates the dagger in Act 2, Scene 1.  During this soliloquy, he sees a clean dagger hovering in front of him, and after he looks at his own weapon, he looks back to see the dagger now covered in blood.  He believes this to be the case because of the crime he and his wife have planned to commit.  Macbeth believes that he stands to benefit from Duncan's death because the Weird Sisters told him that he would become the king, and their first prophecy -- that he would become Thane of Cawdor -- has already come true.  Duncan has named his son, Malcolm, the Prince of Cumberland, heir to the throne, and so it seems that Macbeth will have to deal with him, too, but he and Duncan's other son, Donalbain, flee Scotland after their father's murder because they do not know who they can trust.  With his sons gone, and Macbeth is kinsman, nothing, stands in Macbeth's way to the throne now.