The benefit of growing a cutting of a parent plant is because it is the exact genetic duplicate of the parent. Many variables exist in the DNA of every plant. There are some traits that are expressed and some that are repressed. When a strain of Cannabis has been cultivated and selectively breed for things such as high THC or CBD it has gone through many generations to come to a certain point where the grower is satisfied with the desired traits present in the plant. It is at this point where the plant is considered a sufficient mother plant. From here, cuttings will be made and all the new plants will have the exact same DNA.
Plants grown from seed on the other hand may express any number of differing genetic traits. Seeds from one plant may produce plants with very different expressed traits. One may grow taller, one may have a sweeter or a more skunky smell, the medicinal compounds could also be very different from one plant to another. The main benefit to growing with seeds is when variability is desired. This may be the case when a grower believes that there are repressed genetic traits that would be beneficial to target and bring out in new generations of plants.