Well..... this has been debated before but I'll give you a bit of a summary... .
Here are the theories:
1) Adjusting the valves at the recommended 24,000 mile intervals has caused a few people to wonder why they bothered... . as many of the valves were only a few thousandth's out of spec and they didn't notice any noticeable improvements.
2) It is easy to do and even if it doesn't help anything... . it's good to know that everything is happy underneath those 6 nifty valve covers.
3) Proper valvetrain happiness is crucial..... getting the air in and out in a efficient manner is what we're all about. Having everything adjusted up the way Cummins says it should be helps out our mission, should we choose to accept it.
feel free to add to this list at will... . I am by no means a 'seasoned expert' cajun, creole, blackened, curry, or other spice.....
Matt - 1000 posts!!