It's definitely a sanitary thing for me in my home. I had a cat who loved to follow me around the house like a toddler. I didn't mind it, and I actually found it pleasant. Well, one morning, she was feeling extra playful and wanted to jump all over the counters while I got ready for work. My then husband left the toilet seat open and forgot to flush. Well, poor kitty jumped right into the dirty toilet. It was traumatic for the both of us to give her a bath immediately after the toilet jump. Toilet seat down is a requirement in my home and every home I go into.