Pets tend to destroy a lot of stuff, intentionally or not. If you are renting out an apartment and would have to replace the sofa because a tennant's cat doesn't have a scratching post, versus renting out to someone who doesn't have a cat and that problem vanishes. Pee on the floorboards can get into them and bloat (i.e. pet misses the litterbox, just wants attention or got sick). You can't control these accidents, unless you put them in diapers, which nobody obviously does.