Animals, like people in the world, have a specific function to mantein an appropriate biological rate. I consider that dogs and cats or even other domestic pets have in addition other type of incredible qualities and capabilities.
For instance, many of them can understand a determined situation in wich it is necessary the intervention of feelings: when you are bad, they are "bad", namely, they don't want play and accompany you constantly.
Conversely, when it is happening something bad, they know it and because of it, they get nervious or they start to bark.
Especially dogs are so special; they can help people who need it, althoug you sometimes can´t controle them (since they no longer animals). Blind people need them to guide across the city or simply to cross any small street.
As far as I have checked, animals can become as special as essential, If we see them suffering, we suffer too like it refeers to any other member of the family. Cats are more independents than dogs, but they need a lot of love too.
From my point of wiew, any type of animal can bring a lot of happiness to home, We only have to be with them, and not to leave them when they start to do their needs inside home or they start to bark too early..