Strengths and weaknesses
The defensive concept is pretty basic, but not so simple as to be ineffective. In fact, this defense was very effective, and a modified version of it helped the Seattle Seahawks to their Super Bowl XLVIII victory.
The defense does not require an extra defensive back if the linebackers can provide adequate zone pass coverage (which many can). Nor does the defense require defensive backs to stay stride for stride with receivers off the line of scrimmage (many cannot). So it creates formidable pass coverage that is not entirely dependant upon the personnel package on the football field at the time that the ball is snapped.
At the same time, the ability to run this defense to defend the pass from a base formation strengthens the ability to defend the run. Offenses cannot ‘key’ on personnel packages on the field to audible either a pass or a run. That moves the needle back towards the favor of the defense.
Of course, there are weaknesses inherent in that cover three. One of the big flaws from the Atlanta Falcons forums is that the coverage appears very soft on the outsides. Since some of the deep coverage happens from cornerbacks, a deep route receiver drags coverage with him and that underneath zone is open for quick curls until the next defender shows up.
The other known flaw is to flood the deep zones with four or more receivers, forcing the defense to defend four with three, or to push a slower defensive back deep downfield. If the offense floods the backend of the defense, the belief is that one man will be open. And that is often the case.