Why is it beneficial for the sex cells made at the end of meiosis to be DIFFERENT from each other?

Explanation : Meiosis is reductional division which means the number of chromosomes gets halved. Now if it occurs in somatic cells then it would cause anomalies, as the chromosomes contain vital informations packed in them. In sexually reproducing organisms half of the chromosomes comes from both parents thus leading to variations. So meiosis occurs only in sex cells or gametes. 

In females, meiosis 1 takes place during embryonic stage. During which a fixed numbers of germ cells are produced. At the onset of sexual maturity, meiosis 2 occurs and a mature egg cell is produced - once a month in humans - with the other half of the chromosomes going into another cell called a polar body, is discarded and not used in reproduction.

In males, the generation of spermatozoa only occurs after the onset of sexual maturity. They are produced continously, although fertility declines with age. These cells will live in the reproductive tract of males for a limited amount of time, after which they will be broken down by the body's own system destroying old cells. Cells are destroyed after a certain amount of time because of the risk of damage with ageing.