If you are speaking of the servicing the valves to check adjustment... I went 25,000 miles and checked mine and they still did not need shim adjustment. I have also heard other people checking theirs and finding they needed no adjustment. If they get tight the engine will probably miss on startup and maybe idle poorly as if running on 3 cylinders.
You should probably check them at some point but, it is not like it is just going to blow up if you don't.
Mark