The rim of the glass (also known as the lip) impacts where the wine will land on your palate. If the rim opening is narrow, the wine will land at the tip of your palate, allowing you to taste the fruitiness and acidity of the wine. If the rim is broad, the wine will be taken at the back and sides of the palate where you can experience the tannins and structure of the wine.  Hence, this directly impacts how you taste the wine.