This is a question that should be commonly asked. If fillings or cosmetic bonding is to performed on teeth that are in the 'smile zone' Then bleaching should be performed prior to any visible anterior restorations. Composite shades that are used should match the teeth after whitening is completed.
It should be noted that bonded fillings will not necessarily darken with time, but the bleached teeth they are attached to will. If this happens the teeth may need to have a bleaching touch up, in order to better match their bonded restoration(s).