Division has traditionally been a reliable means of propagating perennials. Probably the majority of perennial species can be increased by this method,and it has the advantage of being simple, as well as not requiring any special equipment or facilities. However, it is probably the least efficient of the propagation methods used with perennials in terms of rate of increase. Still, for some species, such as iris and hostas, division remains the best conventional method of propagation.
Source: • BP News Bedding Plants, Inc.