This is generally known as the beginning of the Patterns, or Kata, but many of the Masters will use a relaxed version of this as their fighting stance. It gives away nothing – your opponent will not know your experience in fighting, and it looks non-threatening. Your opponent will come in closer and will not be on guard as much. This opens up many opportunities of defense.
In this position the weakness is forwards and backwards, so a push or a pull can put you off balance. The large arrow below shows the direction of strongest stance, and the short arrow shows the weakest. You can see, therefore, that while this stance has a good sideways stability, there is little resistance to pushes and pulls. The largest risk to this stance is front snap kicks to the knees, which will easily dislocate them.
In the street, however, you do not want a formal stance. Not only would a straight stance with both hands in front of you look strange, but anything formal would alert the opponent that you might know something and they would be more careful - and therefore your defense will be harder. For this reason, most senior martial artists would take on a causal stance - facing forward, with hands on hips or hanging by their side. If you believe an attack is imminent, putting your hands up in a defensive manner will load up your blocks closer to the attacker and make your defense faster.