Well, fur for some animals is like a huge fluffy winter coat to protect them from the cold. But for some (cats) their fur has natural oils in it, which they need.
Ponies can be therapeutic, but you need a lot of room, in a rural envronment, for animals of that sort. For most people, dogs and cats are much more practical.
One reason amphibians are tied to water is because without it, their skin would not be able to stay moist, which they need for cutaneous respiration (they breath through their skin). When reptiles...
i dont have the exact answer for this but ill give you an example you live in a basement there are a bunch of bugs and two spiders if you kill those spiders there would be alot of bugs