Perhaps one of the most important skills to cultivate as climber is balance. When climbers hear the word, they associate it with lower angle, delicate slab moves, the kind of technical climbing not widely associated with modern bouldering. However, with a little thought, even the most strenuous and steep problem will be affected to a great degree by a deeper understanding of balance. The even steady distribution of weight can prove the key to success not just on a single crux but provide the margin required to link harder moves in a row.
By way of an illustration, consider this move on the Left El Jorge (V11) where Ryan Young is relying heavily on a left heelhook to achieve a long reach off the right hand. The climber has to pull in hard with both the hand and the left leg but crucial to success is finding the right situation for the hips and knee angle so that the load is balanced correctly. When it is, the core muscles just suck the climber into the wall, allowing a better chance at making the reach. Often such seemingly strenuous moves wind up somehow "just happening" much to the frustration of climbers who may spend many tries attempting to recapture that moment. Closer attention to the sensation of balance and equilibrium in this situation may save much time and energy in the end. For shorter climbers a good sense of balance may be key to finding the extra inches needed for a long reach and for taller climbers it may help ease the bunchiness typical on certain types of moves.
In any case, balance is not just necessary, it is part of having fun while climbing even the hardest problems you can. Part of the feeling of flow that is often associated with success comes from a sense of equilibrium and lightness as you distribute everything just right and find the moves much easier than usual.