When defending in this formation it is essential to get the balance right with the wing backs.
When attacking down one side of the pitch, the wing back on the opposite side should not be fully committed to getting in the box but should be hanging wide and anticipating where the ball may go.
It is as if he/she is playing as an advanced full back, which means that you are essentially playing with a back four. To get this balance right is fundamental to the defensive side of this set-up.
To use all the advantages of having extra players in central midfield areas, and to have the advantages of wide players, you must be solid at the back otherwise you will be exposed.
The uncertainty of playing with three at the back is often what puts coaches off playing this way.
If you can get the wing backs playing in a disciplined fashion then you will be always attacking and defending in numbers.
If play breaks down and one of your wing backs cannot make up the ground in time to defend, one of the centre backs will fill-in for them as a defensive full back. The other wing back will also play as a full back, while the sweeper becomes one of two centre backs.
When playing against the standard 4-4-2 formation your sitting midfielder will push up onto one of the opposition’s centre midfielders.
One of your other central midfielders will sit back and pick up the opposition’s other central midfielder.
This will leave you with a spare midfielder who will look to shut the opposition’s full back down.
With the wing backs dropping off, it is one of the midfielders' job to shut an advancing full back down. The two attacking midfielders will alternate this job depending on which full back has the ball. Always show the full back down the line as he/she will have no options to pass to. The opposing wide player will be marked by your wing back and your defenders will be picking up the forwards.
Up front, you expect your forwards to shut the central defenders down and put them under pressure. Their job is made easier by the assistance of the spare midfielder shutting down the full backs.
Overall, this can be a very effective style of play if you possess the right players and they are coached the right way to defend and attack in this system.