Why is hibernation still used?

Because it saves the status of all running programs. I leave all my programs open and can resume working the next day very easily.

Doing a real boot would require to start all programs again, load all the same files into those programs, get to the same place that I was at before, and put all my windows in exactly the same place.

Hibernating saves a lot of work pulling these things back up again.

Normally hibernate mode saves your computer's memory, this includes for example open documents and running applications, to your hard disk and shuts down the computer, it uses zero power. Once the computer is powered back on, it will resume everything where you left off.

You can use this mode if you won't be using the laptop/desktop for an extended period of time, and you don't want to close your documents.

Simple Usage And Purpose: Save electric power and resuming of documents. In simple terms this comment serves nice e.g (i.e. you will sleep but your memories are still present).

Why it's used:

Let me describe one sample scenario. Imagine your battery is low on power in your laptop, and you are working on important projects on your machine. You can switch to hibernate mode – it will result your documents being saved, and when you power on, the actual state of application gets restored. Its main usage is like an emergency shutdown with an auto-resume of your documents.

Hibernation preserves the current system state, and lets you power down completely. Yes, you can boot in mere seconds, but how long will it take you to get your web browser, word processor, chat client, music player, etc. etc. etc. up after that? With hibernation, no time at all.