Imagine I work in a corporate environment, I install some updates, and suddenly things stop working.
People cant access their e-mail, or shared files on the network, or perhaps have no internet connectivity.
I am about to crap my pants.
The business workflow stops, people are getting impatient and the boss is hugely disappointed. Now everyone wants to hang me by the balls.
I cant tell them "Just wait a couple of hours, I'll google a solution".
Now, wouldn't it be great with a rollback feature?
$ sudo apt-get rollback samba
Or something, and a second later, everything is back to normal, everyone is happy and my balls are safe.