Windows PCs and laptops have four power states: mechanical off, soft off, sleep and hibernate.
Mechanical Off leaves only the battery-powered internal clock still running.
Soft Off is the normal shutdown state with a few low power circuits monitoring the power button.
Hibernation is the next lowest. You can carry on from where you left off, usually in less than a minute.
Sleep is a medium low state where Windows, running applications and open documents are stored in the computer's RAM memory and it wakes up and is ready to use in seconds.
Hibernate is better for longish periods of inactivity, a day or two for example.
Sleep mode is useful for short interruptions, from a few minutes to several hours.
Neither mode is harmful, though you might lose data in Sleep mode if there is a power cut; laptops should automatically save data to the hard drive and enter Hibernate mode when battery levels become critical.
If you get into the habit of using Hibernation mode, it is good practice, though not absolutely essential on Windows 10, to shut down and reboot about once a week, to allow Windows to clear cache memories and refresh the Registry.
With thanks to The Daily Telegraph