As a piano ages, its soundboard dries out and often develops small cracks along the lines of the wood grain. Usually, cracks in a piano’s soundboard does not mean the end of it’s life. In fact many, if not most, pianos will eventually develop some cracking in their soundboards. This is often a result of seasonal expansion and contraction of wood due to changes in humidity levels.
The only time cracks in a piano’s soundboard could pose a problem is when the cracking causes the soundboard ribs to separate from the soundboard itself. This can cause annoying buzzing noises and should be repaired. This type of repair, along with the cracks, are often done as part of a piano rebuilding or restoration project because it requires the strings to be removed before the repairs are done.
One type of soundboard that is highly resistant to cracking is a laminated soundboard (essentially a piece of plywood) found mostly in lower end pianos. However, soundboards made from gluing (laminating) pieces of wood together do not sound as good as those made from solid spruce – the type found in better quality pianos. I feel the superior sound produced by a solid spruce soundboard far outweighs its potential for eventually developing cracks. Given the choice, I would always choose a piano with a higher quality solid spruce soundboard over a laminated one.