It's an advantage to both produce sexually and a sexually because by producing sexually, there will be more genetic diversity in the offspring, thus population, and by producing asexually, if there is no potential mates, breeding by oneself can also carry on another generation.
Sexually: Advantage: genetic diversity. Disadvantage: No mate=No offspring.
Asexually: Advantage: No need for the search for a mate/partner. Disadvantage: Basically clones of oneself=No genetic diversity---->leads to high susceptibility to being wiped put by deadly diseases.
