There is a rule in programming that the same place that creates something should also delete it. There are, of course, notable exceptions, but by and large this is also a good principle with respect to things like redirecting output. If the same function that creates the output stream is also responsible for closing it, then you have a natural point for e-mailing it, renaming it, attaching it to something, throwing it away or whatever the appropriate disposition might be.
And, of course, it also tend to keep you from leaving it open and forgetting to close it or closing it somewhere when you aren't really done with it.