How important is it to have a balcony spot?
If you don’t have a balcony there is a good chance that you will see very little, to nothing of the Run (unless you’re in it of course 😉 ). Most of the Run is through Estafeta Street which does not have any space open to spectators and so there are only few places where you can watch from the street level (Telefonica, Plaza Consistorial and Mercaderes, to be precise). These areas start to crowd 2 hours before the Run.
Early during the San Fermin Fiesta the chance of getting a good view is extremely low. Later in the week, the crowds thin out and you can defend a spot in the second row behind the medical staff who are protected by a barrier both from spectators and the Bull Run (encierro). You would have to arrive by 6 a.m. to defend a spot and then possibly loose it again when the police opens the gate to let out surplus runners who then will fight for the spot that you had been holding.
Watch a full length Run from 2009 that will give you an idea of the setting: (the 2nd movie at the bottom of the page).