It is said that power corrupts and sends otherwise decent individuals spiralling out of control as the power goes "to their heads." Macbeth is a recognized, respected and honored commander who is so esteemed by his king that he has been awarded Thane of Cawdor. Lady Macbeth, an obviously influential wife and Macbeth's "Greatness" can show her support and help direct the husband she knows to be inadequate unless he has her guidance.
Unfortunately, however, even the thought of power sends these two into a frenzy - Lady Macbeth especially as she plots to kill Duncan without delay. Macbeth does hesitate deciding to "Proceed no further,"recognizing his "vaulting ambition" as the cause of his desperation to be king. Lady Macbeth is however, very persuasive. The very thought of Macbeth being "so much more the man"(I.vii.) is enough to get Macbeth to focus on thoughts of being king.
The power of the witches to transform Macbeth into a monster has long been a point of discussion. The witches do not have the power to make Macbeth commit these heinous deeds. Their main function is to plant the seed of destruction so as to ensure that "fair is foul."
The power play therefore is really between Macbeth and his conscience. lady Macbeth, although initially goading her husband, loses her prominence as he becomes more power-hungry with each murder or even planning the murders. Macbeth's power is not dependent on his killing women; yet, he does so anyway as he becomes overwhelmed with thoughts of being caught. He must also kill all possible heirs of Banquo as all reason has abandoned Macbeth and the need for power has consumed him.
Power has had the opposite effect on Lady Macbeth. She cannot manage her feelings of guilt and is ultimately driven mad by her conscience. Either way, power has only had a destructive effect on everyone; as victims and perpetrators.