Spaying is a surgical procedure performed by a vet which is used to sterilize female cats.
The procedure is very widely performed in the USA (including by humane societies, animal shelters and rescue groups, as well as individual pet owners), but slightly less common in Europe.
Of course, the principle reason to spay your cat is to prevent an unwanted pregnancy: it's one thing to initiate a controlled breeding program for a sought after breed of cats, but it's quite another to allow your cat to bring unwanted cats into the world, especially if there's already an overpopulation of cats in the area.
There also other reasons why you might want to spay your cat.
The most important of these is that by doing so you can prevent various horome-associated diseases.
For example, mammary tumors are seven times less likely in spayed cats than in unspayed cats, pyometra (a potentially deadly disease of the uterus) is prevented, as are various types of uterine and ovarian cancer.
Spaying also eliminates many types of undesirable behavior because it completely prevents your cat ever going into heat.
If you've ever experienced the torture of a cat going into heat, you'll be glad to avoid this part of cat ownership: no more howling all night, no more attracting mates using strong odourous urine sprays.
Despite all the benefits of spaying, there are some issues that you should be aware of it.
First of all, spaying is a surgical procedure, and like all surgical procedures does involve some risk: the risk however should be small unless your cat has a pre-existing medical condition - consult your vet for more information.
Secondly, there is a slightly increased risk of obesity in spayed cats.
On the whole then, you can see that spaying your cat can offer many benefits both to you and your cat, and that there are not too many risks or negative factors.
Therefore spaying is something that you ought to consider and discuss with your vet.