Avoir besoin de qc is mainly used for concrete objects. It is also more personal than il faut.
Il faut qu'il achète une nouvelle voiture. -- He needs to buy a new car. The focus is on the "buying" part and the overall connotation is a bit impersonal.
Il a besoin d'une nouvelle voitrue. -- He needs a new car. The focus is on the object itself, the car. And it is a very direct and more personal way to express it.