Of service animals and emotional support animals aka pets

The pendulum is now swung in the direction of animals on board aircraft, but I am wondering how this all goes down. With so little space for each seat, how do animals stay in their owner’s space as opposed to encroaching on the space of other ticket holders? A small dog can sit on the lap, but what happens when the dog is larger? Still on the lap? What about a passenger who is allergic to dogs. What happens when she requests a dog-free space? What if a ticket holder complains that a dog is encroaching on his space, will he be removed from the flight or the dog owner? And if they relieve themselves, do the flight attendants clean it up, or the human, or just let it sit and stink up the cabin until someone on the ground deals with it? I know that if I were an FA I might have a problem with cleaning up after an animal. And

Plus I need to keep my “personal item” under the front seat or in overhead while taking off and landing, to prevent it becoming a projectile.
How’s that working for a dog?

PS: I have allergy to cats, tested by blood samples. There are no tests to show the “support” is needed from an animal. That’s just the owner statement.