Hi,
I'm Rodrigo and I'll help you.
The sleep option does not turn the laptop off completely; it keeps the data on the RAM and some components at a minimum power consumption. If you unplug the laptop from the wall, it will keep using the battery and eventually die out of battery.
The best use for the sleep option is when you need to be away from the laptop for a short time.
A better option when you will be away for a long time is to use the Hibernate option; it is not as fast as the sleep option, but it will not use any power, and you can safely unplug the laptop from the wall.
Neither of the options will shut the system down completely, so it is recommended to restart the computer once a week to reload the system files.