Hello Judy -
After my MAC cleared up and my asthma was well-controlled (a long journey) I had no new exacerbations for a year. With my pulmonologist's blessing, to cut back on my 7% saline nebs. First I decreased to one a day, then 5 times a week, now only twice a week. I still do airway clearance each day.
Here is the interesting part - the cut back on days came accidentally - went out of town for an overnight without my equipment. But the next day, I could still "taste" the salt in the sputum I brought up - and even a little the third day as well. That's when it occurred to me that if some of it persists in the lungs, and my body is able to clear mucus with my inhaler and no neb, maybe cutting back would be okay (for me.)
This has been my regimen for over 16 months now and I have had one (minor) exacerbation with a bad cold - managed with a single course of steroids and no antibiotics. During the exacerbation, I nebbed saline daily and continued for 4-5 days after I was symptom free, then went back to my 2 per week.
Also, if I have an asthma attack, or a tighter-than-usual feeling in my chest, I neb daily until it passes - but sometimes just enough to bring up the extra junk in my lungs.

Everyone is different, so feel free to talk to your doc about managing your care in a way that works for you.
Sue