Understand the distinction
Some devices can use electricity outside their main active task, but their behaviour depends on the model and mode. A general statement about standby does not establish the quantity used by every device in your home.
Put it in your home notes
Read the product documentation and any applicable measurement guidance. Distinguish a supplied specification from an actual observation. Follow manufacturer instructions about normal operation and disconnection; do not interrupt equipment with essential continuous functions simply to test a general saving idea.