"Maintaining your installation" question

As I realise this is a nice and way too broad subject, I do have a
question regarding the maintenance of -CURRENT systems in particular.

We see libraries being renewer, bumped up, build and eventually
installed during many -CURRENT buildworlds and installworlds and the
same goes for contributed parts of the base system like gdb (recent
example) and perl and lots lots more.

Is there a 'best practice' for getting rid of leftover 'old stuff': libs
binaries and files as well as (just for example) any updated perl or any
old doc files? 

From time to time I find myself wondering through my lib/, bin/ and
sbin/ directories (and others) to see, using `ls -lt`, which files 
haven't been updated lately. I then doublecheck to see if it is no 
longer in the base and I make an educated guess whether or not I 
can remove the file(s) without killing my system.

Lately I have done exactly this, and I ended up removing the
mount_kernfs (I think I got the exact filename here) binaries from a
4.10-STABLE upgrade I had just done, but what I didn't realize is that
the kernfs was still working and I wondered why it dissapeared from the
base build.

Again, this is even more accurate for -CURRENT systems and I just wanted
to hear any thoughts or proven solutions to this matter.

/Stephan

-- 
Stephan van Beerschoten                    [KeyID: 0x08F12864]
"If you are adminstering UNIX systems and don't master tools
such as make, shell, and perl, then you are working too hard."
  -- Wietse Venema. Fri, 12 Dec 2003