Advantages of asexual reproduction are as follows:
This type of reproduction enable organisms to reproduce without a mate.
It does not require the time and energy that takes to search a mate.
It results in the reproduction of large number of offspring rapidly.
Like in plants, it enables to spread and colonize an area in short period of time.
Animals that are confined to one particular place and unable to look for a mate reproduce asexually.
Stable environments with very little change are favorable for organisms to reproduce asexually.
Sponges and cnidarians can reproduce asexually and sexually.
Asexual reproduction in sponges occurs when a bud on the side of the parent sponge develops into a small sponge. The small sponge breaks off, floats away, and attaches itself to a new surface. New sponges also may grow from pieces of a sponge. Each piece grows into a new, identical sponge.
Polyp forms of cnidarians, such as hydras, reproduce asexually by budding. The bud eventually falls off of the parent organism and develops into a new polyp.
To learn more, see this study guide for invertebrate animals (pdf) from Glencoe.com.