Anyway, the point I was trying to make:
The saluting is a two-way courtesy.
If you neglect to salute your superior, he will get angry with you.
If he neglects to return your salute, his superiors will get angry with him.
Another 35 year-oldish memory 
[the days of Ronald Reagan and the promise of a 600-ship Navy]
My remembrance is as a Naval Officer with 3 of 4 active duty years on an aircraft carrier. Salutes were mostly done when coming aboard/going ashore while in port or at anchor, at morning muster (a formation) and when assuming or being relieved of a watch.
I’d say salutes are a requirement, not a courtesy. One does not get written up for violating a courtesy but do for violating a requirement (while some requirements may be spoken of as courtesies, there is a standing order or article of the Uniform Code of Military Justice behind them).
Salutes between junior officers: the philosophy I recall was *Seniority between junior officers is like virtue among prostitutes - nonexistent.
Nod, smile & salute and get your 20 (years).*
dba fred’s career Marine father
So that’s what it is!
By chance I was watching an American action/crime genre movie last week, and the masked female criminal was making a weird elbow-height movement when she wanted the crowd to move along. It just looked odd to me. I could see the context, but the action was meaningless: it didn’t say “move along” to me at all.