When installing something in customer's home, for example installation an Air Con, plumber or electrical works, they left the rubbish in customer's home. This will make customer put up extra effort to clean the contractor's rubbish, of which they should clean everything before the left.
Here are few example for illustration.
The contractor shall take away anything related to their job and throw away accordingly.
(In the case above, the other contractor asked the installer to leave these boxes as they wanted to use them).