ICA: Hibernate vs Sleep

  Hibernation takes a snapshot of everything you got on RAM which means that everything you're doing and save it into the HDD. It does not use any power as it is the same as powering down a computer, while saving the previous state while you are working. It is way faster compare to completely shutting down and re-powering up the computer.

  Standby resume faster than hibernation but it does consume a minimal amount of energy. As it basically shutdown the computer except the RAM as the session is stored in the RAM. It resumes way faster than hibernation and this is a brief explanation from Lifehacker 

Your machine recovers quickly as your data is stored in RAM. The slower part is waking up the peripherals. Although your machine is in "standby" the power has been cut to items such as your hard drive and monitor. You're running your machine in a very low power mode, but it is still on. This mode can be useful if you're on a notebook and need to conserve your battery while you step away.

  In conclusion standby is used if you're just leaving for a short moment for example for lunch, hibernation is used if you're leaving your computer for a few hour or more.