i would think that if you actually get the oil filtered down to anything close to 1mic, you will almost never change and onboard filter; so why not use one?
If you need to use some oil on the road or have a problem with your at home filter then you have the cheap insurance of the on board filter allready set up.
In driving my mercedes 70000 miles i was VERY slow to correct mistakes in the planning and original plans (adding to and adjusting my set-up) so on my new project i am gonna do it right first time.