Deadheading is the removal of spent bloom. Roses are most often deadheaded to encourage rebloom. Varieties that bloom only once a year do not require deadheading. Removal of old blooms prevents the formation of hips. In some, but not all, roses, the growth of hips appears to inhibit rebloom. Sometimes roses are deadheaded because the faded, spent bloom is unsightly and disreputable looking.
Because different classes of roses bloom differently - - whether singly, in small clusters or in enormous sprays - - and because each rose looks different with old flowers on the plant, hard and fast rules do not apply. Some roses drop all their petals neatly and move right ahead to the next flush with no encouragement. Others refuse to rebloom if there is a single hip anywhere on the plant.
One rule does apply: to deadhead properly, the rosarian can easily sacrifice one flush to study the growth habit of a new rose. Cutting every rose back to the next lowest out-facing 5-leaflet budeye is not required with most non-Floribunda, non-Hybrid Tea roses. Simply wait and watch for new growth, and your rose will have taught you where to deadhead. See the photo tab for an example.