I work as a manager and will totally agree with your point.
Yes how you dress does affect your personality. Being dressed in Suit makes you professional . Doing up you hair nails and having a bath daily building your confidence on meeting people.
Working in an office needs a professional outfit
Working out doors can have a dress code too for comfort and professionalism>
are you representing a company (Sales / HR Etc. ) You need to be formal or in a suit.
If your an onsite engineer Jeans and you basic PPE does perfectly well

What you wear does define you !!