I never thought this was some sort of taboo "nobody talks about this" topic, though. It's been openly and freely discussed for longer than I've been alive.
Although not entirely appearance related, Slow Ventures put out books and seminars to help founders not only look and dress better, but also be more intentionally professional, that seems to suggest there's a drift away from startup swag to sport coats.
That got me wondering if aesthetics like hair transplants, breast implants, and similar were as common in tech as they seem to be in Vegas, Miami, or LA, but that it's just not discussed as much.
And that aspect of appearance is what various advisors are talking about when it comes to appearance.
If you're wanting to get, say, a group of investors to give you a pile of money, or to woo a hotshot dev over to your company, or whatever, what you're facing is a communications problem. How you look, speak, dress, and carry yourself is a huge part of that communication. Through them, you're communicating something -- whether you intend to be or not -- so the point is that you should be communicating with intentionality.
Different subcultures have different aesthetic languages, and you do best by speaking in the language of those you're addressing.