There was an interesting article on here last week about trying to replicate primitive carpentry for archaeological purposes. An illustrative example of the why was that in their first attempt they broke all their stone axeheads in the first hour; after they got some practice they were able to estimate the acreage they could clear with their techniques. Reconstructions both tell you what you got wrong and provide new information about the capabilities of our ancestors, as well as providing context on the archaeological remains.