It is important for cats and kittens to have stable homes because if they don't, they are in danger of injuries, diseases, and becoming feral.
If a cat can't find a safe home, they are in danger of a lot of things, like dieses, fleas, and starvation in the wild. If they can't get adopted or fostered in shelters, there is a large chance they will end up euthanized.
When you foster a cat, the cat is essentially yours, but you can give the cat back if you are allergic to it or if the cat doesn't fit your preferences.
When you have a cat, you have a little friend that you can spend time with. You can hold them, hug them, kiss them, and play with them. They are also good listeners.
A cat will be there for you through the good times and the bad, and can keep you company. You can always play with your cat, which can keep you entertained for long periods of time.
A cat only needs a few things to be safe - food, water, and a litter box. They also generally require less attention than dogs, and you can generally leave them alone for long periods of time.
It is much cheaper to adopt a cat/kitten from a rescue group than to adopt a stray. Although it may seem more expensive due to the initial fee, the fosters have all of their vaccines and surgeries, while a stray does not. Any necessary vaccines your new cat needs will not be paid for.