Balance, as in a balanced diet...
A balanced diet means that we eat enough of different types of food without eating too much of certain categories. Similarly, a full life means that we must tend to various parts of our lives (family, work, health, relationships, friends, hobbies, exercise, etc.), all of which are important parts of a whole.
When some see the term "work-family balance," they think of balance as in a scale, seesaw, tightrope or balance beam in which there is a single, hard-to-find, precarious equilibrium point between two opposing forces. Thinking about balance that way leads people (including managers and employers) to think about work and family solely as trade-offs. I think this is problematic, and this is the reason many work-family academics eschew this term.
...as opposed to a balance beam
Sometimes we need to prioritize one over the other and temporarily slip out of balance -- there are inevitable ebbs and flows in both home and work. The use of a tightrope metaphor frames temporary imbalance as a failure -- in fact, on a tightrope, anything less than 50/50 means a perilous fall. If, instead, we think about a balanced diet, eating too many carbs one day can be balanced out by extra salad the next. And it also helps us recognize that we need many food groups to be healthy.
Most importantly, however, we need to stop seeing work and family as "either-or." Time for work and for family are both very important components of a full, meaningful life. If we don't reflexively see them as opposing forces, we may come to understand that both can enhance the other in helping to build a balanced life.
What do you think about these metaphors? How does this relate to your work-family juggle? Let's discuss in the comments section.