Is There Any Benefits For Plants Or Organisms Which Produce Asexually?

Plants and organisms which reproduce by themselves actually seem to be at a disadvantage.  It would be easy to assume that because they can reproduce by themselves, that they would be able to multiply at a huge rate, compared to other life forms.  However, scientists now believe that  when some form of sexual activity with another takes place, the gene pool is 'widened' and this actually means that the species can evolve more quickly.  In short, the offspring of a lifeform is genetically different from its parents and so not likely to succumb to the same diseases.  
If a lifeform 'self-reproduces' then the offspring is genetically the same.  So would easily be prone ot the same disease as the parent.
Also if a lifeform reproduces by itself then it has to invest more of its energy in doing this, than if there has been a contribution from a sexual partner.  Again, this leads to a less strong gene pool and so is less desirable!