Fabrice Grinda pointed me to a great article in FORTUNE:
Cross-train your brain: The pursuit of excellence need not be single-minded. That serious hobby of yours? It can, believe it or not, make you better in everything you do

essentially — there is a huge advantage to being a mile wide (with a few deep sink-holes too). this gives you the opportunity to spot trends and look for patterns. it might also prolong your life.

Thomas Friedman makes this analogy in foreign policy. while there are a great deal of specialists, the generalists like Friedman who know lots (but is not an expect) about lots of countries (and he also understands technology, trends, economies, politics, environment, financial instruments, and more) can build pathways between random pieces of data that others wouldn’t see. Peter Thiel is a good example of a business person who does that.

Fabrice sums up:

To some extent, this is counter-intuitive – you might expect to perform best by putting 100% of our efforts into a single pursuit. However, recent evidence suggests that is not the case. Your behavior shapes your brain and the benefits of practicing one skill are not limited to that skill alone, they can be transferred, and the more things you know something about the more there is to transfer. As Alvaro Pascual-Leone, professor of neurology at Harvard Medical School says: “If you practice multiple things you actually get better at any one of those things.”