Interestingly, sometimes Sellers leave behind things that they think the buyer might want, or is just too difficult to get rid of. For example, I have often seen paint cans left for the new buyers. In theory, this helps the new buyers identify what the colors are in the home if they need to repaint. For sellers, paint is notoriously hard to dispose of so in a perfect world, this works for both sides.
The problem is that often the paint is years old, moldy, and/or dried up. A paper list of paint color information works much better. The buyer ends up trying to find a way to get rid of all the old paint.
I also have seen grills, porch furniture, swing sets, and many other items left at the home as they leave. Luckily, the new 2019 contracts specifically state that not only does the home need to be "Broom Swept", but it specifically states that the seller cannot leave anything behind that has not already been agreed to be left behind in the contract. It also says that objects in the home cannot be removed without being replaced with substantially the same thing.
In order to stay out of contract difficulties, make sure you have a professional Real Estate agent at your side.