Why adopt an animal when you can just go out and buy one? Why make an application to find animals when you could go to any old local pet shop and buy an animal?
Adopting an animal saves a life - animal shelters and rescues cannot keep the animals they receive for their whole lives. Limited space, monetary issues, and lack of staff means that animals are euthinised after a certain amount of time at a shelter or rescue. If you adopt an animal, you help both the adopted animal, and the animal which will fill the adopted animals space in the shelter or rescue.
Animal rescues are full of healthy animals. They examine, treat, vaccinate, and neuter animals when they arrive, or before they leave. They also get to know the animals, allowing them to inform prospective adopters about the animals personality, temperament, behaviors, and needs. This means that there is less risk of the people adopting the animal finding they are incompatible.
Animals generally don't end up in shelters and rescues because they're badly behaved, aggressive, or have been abused. Most animals are given to shelters and rescues because their caretakers couldn't keep them due to issues like getting divorced, not having the time to look after them, moving to a house where animals are not allowed, having children, not being able to afford their care, and so on. They haven't done anything wrong, they are just unwanted by their original caretakers.
When you get an animal from a shelter or rescue, you save money. Most animals will already be neutered and vaccinated, which saves the cost of having the operation and vaccinations done at the vets, which can be very expensive. You won't be charged for the animal like you would be in a pet shop. The shelter or rescue would only ask for a contribution towards the cost of looking after the animal while it was in their care. If you cannot afford this, most shelters and rescues are understanding.
In addition to these reasons, a lot, if not all, animals in shelters or rescues will already be toilet trained, sociable, friendly, comfortable around people, and eager to find a home. The animals in my family were all from shelters, and they all came pre neutered, vaccinated, toilet trained, and friendly!
While people purchase animals from pet shops, animals that need homes go without homes. Most animals who need homes are unwanted pets. It makes sense to give a home to an animal which needs a home rather than buy a 'brand new' animal which creates more demand for animals to be bought, which leaves more animals in animal shelters or with rescue operations. Most animal shelters, and especially rescues (which are usually run by an individual) can't afford to keep animals for their whole lives, and they're put down if they aren't able to be found a proper home.
The pet trade is ethically questionable. I shan't go into the details of puppy (kitten, hamster, rat, fish, chinchilla, ...) farms, but the process goes something like this. Pet shops obtain the animals they sell from large scale operations / breeders. The breeders breed animals. They breed animals on a large scale. Their concern is not with the welfare of the animals, but their production rate of babies. This could be compared to a battery egg farm in terms of production values - battery farmed eggs are cheap, but generally low quality, and not very considerate of the chickens. Animals from these breeding operations are cheap to the buyer (the pet shop), profitable for the seller (breeder), the product is low quality (Poor immunity, inherited health issues, physical issues from generations of inbreeding, ...), and there's not much thought towards the animals.
