I agree with all that Jen posted as for reasons. I also have to add that it just plain isn't fair to your neighbors for your cats to be running loose outside. They often will use flower beds as litter boxes...
You know what, that isnt a problem here, because we have a HUGE hill in the back like a mountain kinda, all the cats use that . And noone cares if a cat was in their yard because everyone on our street owns at least one cat .