Genetic Algorithms - Why wouldn't we use the principle of Elitism?
It increases the convergence speed of the GA, which is a double-edged sword. You want the algorithm to find good solutions quickly, but not so quickly that is has not been able to sample sufficiently large areas of the space that it's not just doing a very local search around the initial population.

Another option that can work well is to be elitist, but try to intelligently figure out when you've converged and should introduce some diversity.