Yes, you often want to do this just to make sure you're overriding the server's defaults.
If you want all your notices logged into an error file as well as the fatal errors, and the server defines the default error level as E_ERROR, then you'll have to override the default error level.
Horrible article.
I did this one recently, because I needed to use some PEAR modules that produced notices under E_STRICT. I somehow think all of these have similar exceptions.