Well, while not being a hardcore clothes horse or a fashion guy (I’m a blue-collar worker), I do agree that the appropriate clothing for the situation is de rigueur.
As to the question in the thread title? I suppose it’s for me, really. When socializing, I know when and where to wear a navy blazer, which kind of sportcoat, or even a safari-type jacket, which trousers, which shoes, which tie and how to correctly tie it at the precise length. When and where a suit is required, and the necessity of correct tailoring.
Grooming? Well, I think society in the US has taken some pretty large steps in recent decades, towards a kind of “manscaped” carefully “scruffy” look, if not the actual lumberjack or the hipster moustache (I’m very proud that I followed through upon losing a bet at work with wearing a John Waters moustache, using an eyebrow pencil and everything…looked…“good” Maybe not Chuck E Cheese table for one good, but it was kind of fun!).
I personally follow the lead on this one, and while I can give myself an extremely close shave with a safety razor and some platinum blades, most days I just give a trim around the “beard” line (beardlet?). Shave it clean every few weeks or so when an actual beard is pretty much full-on.
Dental hygiene I do for myself, 100%…I don’t give a damn if people think my breath is wolf or not, but I’m old enough to that it’s wise, in my case at least, to mitigate receding gums with regular use of the waterpik, scrupulous flossing, and proper use of the toothbrush.
I did enjoy appearing in court several times (as a defendant) last year and, without fail, someone or other (a clerk, another lawyer, some random person) would ask “who are you representing?” or just “are you a lawyer?”). That was just wearing a tweed jacket, or a navy blazer, some kind of wool trousers, leather shoes, and a tie.
Is it for me or for others? I don’t know. Personally, I don’t much care for most people, and often outright despise them, but I think decorum is important for some abstract idea, I suppose. I know what’s right and I cleave to the standard.