Why is it important to allow for expansion in hardwood floors?

Allowing for expansion in hardwood floors is crucial primarily to accommodate temperature and humidity changes. Hardwood is a natural material that responds to environmental conditions; it expands when it's warm and humid and contracts when it's cold and dry. If there is no space for this natural movement, it can lead to a host of problems, including warping, buckling, or cracking of the flooring. This can not only damage the aesthetic quality of the floor but also compromise the structural integrity, leading to more serious repair issues in the future.

The other options, while they may be relevant in certain contexts, do not address the primary concern associated with the natural properties of wood. The need to prevent squeaking sounds and to accommodate furniture can be influenced by how the floors are installed and maintained, but these factors are secondary to the critical issue of environmental adaptability.