So that if you want more or less variation you know, in a general way, how to reach your goal. How any trait you many desire is more likely to come from related parents show possess the trait than from unrelated parents who possess it. This plan is also more effective in correcting defects. That is, mating your little bitch to a related sire who is strong where she is weak, than mating her to an unrelated sire who is strong where she is weak. Why increased homozygosis is important and desirable at this stage of Shorthair development.
Fire feeds and warms, it also destroys.
Because it destroys we do not abandon its use, it has too many benefits. We use it much but we use it cautiously, making every effort to gain its advantages while guarding against its hazards. If our vigilance slackens we are destroyed. Some would prefer not to live so dangerously. Superior phenotypically, from what we can see.