Functional for what walking through airports?
The side cap is distinctive, it tells the branch and tops the uniform and best of all, it isn’t a hat that a GI has to figure out what to do with when it is removed throughout the day, you don’t have to find a place to set it or hang it.
The hat is very popular and I think all the branches use it, the military has used it since WWI.
Why does one wear a hat at all? To keep the sun out of your eyes, or the weather off your head, like when you're outside, doing military stuff, or whatnot.
I'm glad the garrison cap worked for you, but I hated their look and uselessness. Diversity is our strength.