The strategist in me says fall down before the score and kick the extra point length fg, but then you think - what if something happens. If you are ahead it is a no brainer, different story if you are behind.
I do recall one game (don't remember what it was), where GT was going to kick a FG - but on third down. Snap was bobbled but GT landed on it, they were then able to set up again and kick on 4th down and made it for the win. Of course to do that you have to have a TO in your pocket and leave enough time so if something does go wrong the clock doesn't run out on you.