Standard expo is 0, which is linear steering. We just add a bit of expo. So the difference isn't that big, but it is noticeable (just make sure you use the right expo - if you add expo in the wrong direction, your steering will be much quicker in the initial steering, which is quite the opposite of what we want :P).
So our steering is still quick - if we yank out that steering to full steering, the speed of the servo will still be quick. Running a bit of expo just makes it easier to make the smaller corrections.
While this is very effective in onroad, I do feel that we don't do a lot of small corrections in offroad, and less expo might do it (lets say age/2).
Using the age is just a rule of thumb. We all drive differently, and because of that need different settings.