Answer:
Several
Step-by-step explanation:
noise reduction, less waste (animal poop, toys, etc), less destrcion of property (chewing, scratching, etc), you could also argue reduction in outdoor allergions or even increased saftey and site statistics for animal bites. You could also look at feral animal colonies and look at how outdoor animals infulence that or even how outdoor animals inpact the local ecosystem. You could look at this in several lights depending on the effect you want from the audience (ethos,pathos,logos).