what has Macbeth to gain from having Banquo murdered?

Macbeth believes that in murdering Banquo,he eliminates the possibility that Banquo might become king. The witches describe Banquo in the following way:

"Lesser than Macbeth and greater," "Not so happy, yet much happier," and a man who "shall get kings, though [he] be none"

Macbeth is ridding himself of competition.