Are there any positive effects brought by la nina and el nino?
Basically any weather pattern will bring both positive and negative effects. La Nina and El Nino tend to shift precipitation patterns such that as one are sees drought, another are sees enhanced precipitation, possible ending a drought there. Temperature patterns are also altered thus some areas see colder than average temperatures which can target pest-infested areas, while other areas see warmer than average conditions which can reduce heating needs and other expenses typical of a cold climate. There are numerous other examples, so the answer to your question is yes, at least in some cases.
