REALLY IMPORTANT NOTAMS tend to alert pilots to RESTRICTED AIRSPACE or AREAS OF UNUSUAL AIR OPERATIONS. You can't fly anywhere near the President of the United States, the movements of which can change from day to day.
We get NOTAMS about military aircraft operations; often military airspace which is usually permitted may be shut down for a week or so.
Wildfire tanker operations or other natural emergencies can close an airspace.
It's quite dynamic, all on top of the scheduled flight plans and routes.
If you like lots of daily mail, become responsible for the operation of a Cessna 172 (Skyhawk), the type of aircraft with the most units built of any, ever. Endless variations.
Unending stream of paper NOTAMS via US first class post office... at least, when I had a 172, 20 years ago.
These notices are exactly like a recall notice on an automobile: get someone to validate the steering wheel etc. I would suppose that many HN readers have gone through the car hardware remediation process.
I would suppose that this class of NOTAM, although in my particular case the most common, are not immediately relevant to a total Ground Stop Order for the USA. But -- consider that airline and other commercial operators may have their own internal requirements that could ground a fleet in the absence of an ability to state that they have complied with all relevant FAA NOTAMS. Oh, the liability!!
We get NOTAMS about military aircraft operations; often military airspace which is usually permitted may be shut down for a week or so.
Wildfire tanker operations or other natural emergencies can close an airspace.
It's quite dynamic, all on top of the scheduled flight plans and routes.