What does all this mean to a field technician? I'll tell you. It means two things if he/she understands the concept:
(1) They'll get two-points towards passing a 50 question entrance exam.
(2) They'll be able to impress their non-nuke friends at the next keg party.
A field tech will not estimate a dose rate by pressing buttons on a calculator. Never have, never will. He/she will grab an RO2 or 2A, check the cal date and battery level, make sure it has a current source check and then go out and swing it!
1) If all this means to you is 2 points on a test, then that is probably all you will ever get from it.
2) Your non-nuke friends will not be impressed by this any more than the fact that you are a nuke in the first place. You could make a bunch of words and numbers up and they would never know the difference.
For the average tech, you are probably right -- you don't need to be able to do this calculation, just like you don't need the 6CEN thumb rule, shielding half-value layer calculations, or most of the nuclear science that you find on tests, either. If you want to be an average tech, you can ignore all of that extraneous stuff. If you want to be above average, it certainly helps to know your craft better than the next guy. I have been able to work a wide variety of RP tasks that were 'above average' because I demonstrated a knowledge level higher than the average tech. I happen to enjoy swinging a meter and have turned down ALARA jobs for job coverage slots. But, I have also held ALARA slots, Rad Engineer positions and am teaching again because I could demonstrate an 'above average' level of competence. I get paid more, arrive first, stay longer, and do more interesting work because I took the time to understand all that stuff I didn't need to know. Oh, yeah... I sweat less now, too.
Taking the NRRPT (and passing it) shows that you care about your craft and that you want to know more than just enough to get by. You will not get to practice all the esoteric points often, but when you do it is satisfying that you know how to do it. It also helps when you understand 'why' and not just 'how' you do what you do. Or maybe that is just me.