This unique and highly sought after pattern in wood can greatly increase it's value for fine wood working. However it is a fine line to walk.
Spalting is caused by a fungus that occurs mainly in hardwood species (especially Maples and Oaks). Ideally you want to harvest it before the fungus has decayed the wood beyond use.
Even if harvested at the ideal time, it is not advised to use the wood for anything structural such as table or chair legs. It should be considered purely decorative.