What’s good about Safe Sleep (hibernation) in Macs if the system will open apps anyway?
The system will re-open apps, but it won’t open unsaved documents. If you shut down instead of hibernating you have to decide whether to save or discard every unsaved document. 

It’s also quicker to hibernate/wake than it is to shut down/boot. 

This is a really bad example, but here it goes:


Hibernate is like Han Solo being frozen in carbonate. 
Logging in is making a new baby and growing him up to be Han Solo. 


(As if either were possible in a world other than science fiction). Logging in starts a sequence of application starts and not all apps save their state so hibernate generally gets you closer to where you were without keeping the system alive and consuming energy during the rest period.