The main point of balance is that you are a more complete human being when you participate in a wider range of activities. Even if that just means you're a better developer because you stepped away for an hour or a week and got a new perspective. Just because you're not miserable only doing primarily one thing doesn't mean you wouldn't be happier if you forced yourself to learn or see or try new things at regular intervals. You'd most likely be much more interesting to those around you too.