I think they really started doing the "Tune up" thing a little more often in the 90's. They use to not be as aggressive with CF even when they knew the life expectancies. However, with advanced medicines they don't mess around much anymore. Well I should say it depends on your CF doctor. Our doctor in Dallas Dr. Michael Brown is a great doctor. He will give it to us straight and not mess around with the disease. At the first sign of my son's PfTs going from upper 80's to the 70's and fever with cough, he will go into the hospital no questions asked. Sometimes we are suprised when my son goes in for a regular 3 month check up and he seems to be doing fairly good with a slight bit more cough, he will want to do a "Tune Up" every few years.
I guess it depends on where you go. But if you have never had a need for a Tune up then great! But if you are noticing your lung functions down into the 60's and dropping year to year, and your doctor has never put you in for a Tune up... you might need to seek advice from a different doctor. Its not worth messing around with.