They can make a bit of a mess (alive I mean, I imagine they make a bit of a mess dead too). We have one or two visit our garden – I don’t think they live here because I don’t see them very often… and I work at home so I spend a lot of time staring out of the window 😆.
You’ve got to be pretty careful about leaving food around as above. I’d squirrel-proofed one of our bird feeders after the local squirrel polished the lot off sharpish by putting a cage round it and dangling it clear of the branches of the tree it’s in. Later spotted the rat casually sitting in said cage munching its way through the contents of the feeder.
We also have loads of windfall apples at the moment, but they’ll be gone soon, rotted or eaten by the birds, so thought that’s why I’d seen them around again. But then I found they’d got into the storage container where I keep the bird food and eaten their way through a bag of seed. They obviously liked the nice sheltered place with lots of food so had started building a nest with all the chewing of stuff that comes with it. Droppings, and presumably urine, everywhere so disinfected everything.
So not giving them places to live is a good idea too. When I built a new shed/deck I put chicken wire round the base to stop them getting under it. Don’t know whether it’ll be enough since when I lifted the paving slabs that were under the old shed, there was a network of tunnels with chewed plastic “bedding” in them underneath.