Why have ? I have this question in biology. Looking for opinions. Scientific ones.?

Why have ? From an evolutionary perspective, if survival of the fittest means that those populations that can produce more offspring are more likely to survive, why do so many speices use meiosis and ual reproduction if aual reproduction is faster and more efficient? Why is this good for the evolution of organisms? What are the advantages and disadvantages of ual reproduction, compared to aual reproduction? Discuss this in terms of competition for resources, survival of the fittest, natural selection, and genetic variation.