For those that do, why do you put clothes out in the living room or dining room? Doesn’t everyone else go bed > bathroom > bedroom to dress > breakfast > out? Surely that’s an extra trip downstairs to get clothes, then take them back upstairs!
Presumably those families get up, get washed, go down to breakfast, get dressed downstairs, leave as opposed to taking the clothes back upstairs ... If you have younger children it makes sense to just have them change downstairs in the living room where you can supervise/help/chivvy along/bribe the child to get dressed whilst also tidying up from breakfast and getting ready for the day yourself. Older children who want privacy can obviously change in their room but then those children would have their clothes laid out in their room in the first place.
For those that lay them out on the floor, aren’t they at risk of being stepped on/sat on by pets and messed up?
Presumably those who do this either don't have pets or have pets that aren't allowed in the bedrooms or wherever the clothes are laid out so it's not a concern ... My parents have pets but they very rarely go upstairs so, whilst they don't leave things on the floor, if they did then there would be no fear of them getting dirty as the animals don't come upstairs and they're a "shoes off at the stairs" household (all of downstairs is hard flooring so they don't mind shoes being worn, but nobody wears shoes upstairs which is all carpeted) so floors are pretty clean in bedrooms.
For those that put multiple outfits out (e.g. for the week as some have said) do you have a lot of space or are there clothes hanging all over your house?
I used to have all of DDs uniform separated out by day for the whole school week but it was just a small plastic drawer unit that slotted into the bottom of her wardrobe so took up no extra space ... In the holidays, especially the long summer holidays, I'd use the unit for seasonal things like swimsuits/shorts/sandals etc to make them easily accessible for DD to get herself.