You leave fewer openings when casting a spell.

At 2nd level and every 2 levels thereafter, you gain a bonus feat in addition to those gained from normal advancement. These bonus feats must be selected from those listed as combat feats.
Whenever you gain a new bonus feat, you can also choose to replace one of the bonus feats you have already learned with a different bonus feat. The feat you replace can’t be one that was used as a prerequisite for another feat or other ability. You can change only one feat at any given level, and you must choose whether or not to swap the feat at the time you gain the new bonus feat.