The simple answer is: Yes. It does work. It prevents the birds from reaching the grapes and thus, directly lowers the bird damage to the grapes. This is especially the case if there is shade near the vineyard where the migratory birds can stay. It helps to change the pathway of the birds.  If the birds used to pass over the area and feed on the grapes, using side netting will stop the birds from doing so. This might truly be the case if there are other types of farms nearby. It is effectively the best method in medium and low-pressure situations. The netting usually stays till the fall when the grapes can be harvested.