It takes time because you don't lose data, if you want a quick update you do an altboot, but then you have to set each machine up from scratch, you are trading fast update (where your job is to do nothing) with quick update (You spend an hour setting it back up from scratch, clone files can't be used from 072 to 073 releases)
As I already stated, it will fix Airprint/MOPRIA.
Some fixes for SMB with server 2008/2012/ Win 10.
Adds App gallery
Speeds up UI and EIP connections
Security updates
Better SHA-2 support.
But there are about 173 fixes(Some are all connectkey, some are not), I can't bother listing them all individually.