DISADVANTAGE #2. “Vegetative reproduction has the potential to interfere with pollination and mating, resulting in reductions in the quantity and quality of offspring. This situation can occur when clonal dispersal disrupts the functioning of sexual systems, leading to the absence of mating groups required for outcrossing, or where very large clones experience fitness costs (inbreeding depression and pollen discounting) associated with geitonogamous (between flower) self-pollination because of large floral displays.”
http://www.pnas.org/content/112/29/8859.full