Its definitely needed.
By default the package manager will not overwrite files that are different from the defaults
(such as something you edited, or that is particular to your system like language and password)
So instead of clobbering those files it makes .pacnew files.
In the (rare) cases it does it the other way around its a .pacsave file.
This just comes with the rolling.
It is the users responsibility to take care of these things.
If you dont … little and big bugs can pile up over time.
Some you may not notice, and some like PAM may be a near instant show-stopper.
So … here are some quickies:
List pacnews
pacdiff -o
And I like using meld … so to compare only view (hit v for each instance)
DIFFPROG=meld pacdiff
(of course you could set your DIFFPROG variable elsewhere and not need it here)
PS … here is an example of meld and a file you should definitely not merge or overwrite:
