If you happen to be hit by a bus, chances are that no matter how clearly and completely you write the text of your documentation, an emergency situation will come up before your (hopefully more bus-resistant replacement) will be able to read it all.

That isn't to say that you shouldn't bother writing it... By all means, you should.

I'm a strong proponent of application flow diagrams. In a pinch, it's much easier to see which other things the little picture of 'sqldb19' has lines running to, than to scan through pages of text, hoping that you don't miss a reference to 'sqldb10-20.'

Note that sqldb19 doesn't need to be a seperate server for this to work. I apply this type of graphical overview to things like cron jobs that summarize data, to be able to know which reports will be wrong if suddenly the cron jobs all stop. It's easy to trace the lines to the sql server, then to the web servers that query it.

Eh, I tend to be pretty visual, so maybe this is just me...