Vetch, Ged's BFF, gives Ged magical power over him by sharing his true name, Estarriol. Best friends share everything, even true names. Also in the tradition of school fiction, Vetch isn't super interesting all by himself. Think about Harry Potter and Ron Weasley in the first Harry Potter book: who's the better magician? Whose story would you rather listen to? The hero's best friend is usually there just to help the hero be heroic. Here's how we know that Vetch is simple and not exactly ready for primetime heroics just yet: when we meet him, he's talking about food (3.35).
But what's so wrong with food? Ged may be searching for great mystical power, but Vetch really knows how to live a balanced life. He has a family (well, siblings), and a nice house, and he does a good job as a magician for the town. Seriously – would you rather be the tortured, brilliant magician or the happy, average one?
Vetch is pretty useful here as an example of a magician who lives a balanced life, even though he's not an old man (like Ogion or Nemmerle). But there's another, rather important reason why he's in this book: he gives Ged the self-confidence to carry on and do all those tortured, brilliant things he must do.