Reason #1:
You're saving two lives instead of one.
As Sarah reasoned, "If it's kitten season, that's one more kitten that will get a home instead of growing into an adult which will decrease its chance of getting adopted." It is entirely true that kittens are much easier to place than adult cats, and the 15-month-old cat you see in the shelter today is very likely a holdover from last year's crop of kittens. Another way of looking at it is that it's better to get all the kittens adopted out right away, to give the older cats a better chance at finding homes.
