How can natural chimerism be advantageous to a species?

[Erebus]

Genetic chimerism is a condition in which a single organism is composed of cells with more than one distinct genotype. In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types. Elves inhabit this world, but do not possess magic in this reality. Instead, they are all what can be genetically considered chimeras because they have a strange way of reproducing.

When partners decide to conceive, A male must add his genetic material at different intervals throughout several years to the female. Genetic material could come from a single male or various ones with no connection to each other. The developing child is slowly "built" with the genetic material of one father, or the makeup of several different fathers. After enough "material" has been collected, the embryo becomes fully formed and the gestation process can begin.

This genetic anomaly among humans is the standard norm among elves. What advantages would this provide to elves as opposed to other single-insemination species?

 

[K.S. Crooks]

Some ideas on advantages to having many "fathers": more likely to have some resistance to more diseases, may have a greater variety of talents (though not as strong), or the female could select males all with a given talent and load up on that quality, prejudice may be less since many in their society will have a variety of ethnicities in their genetic makeup, a female has even greater control of when she reproduces, a one-night-stand is less likely to lead to a child being born, over-population would take longer, more difficult to have twins.
Depending on how it completely works the more "fathers" a person has there could be a greater chance of genetic disorders. This can be avoided if chromosomes are kept intact...sorry if being too scientific, I probably wouldn't mention this in the story.
Hope this helps.