It is much easier, and quicker to install prefinished hardwood. The Process of a creating a site finished floor can be time consuming, going through the process of sanding and staining the material on site. By contrast pre-finished floors are ready to go as soon as they are installed.
Pre-finished hardwood provides more durability than on-site finished hardwood floors. When the factory applies the finish treatment to the wood, they are able to use very powerful chemical sealers. These are applied by commercial processes which are not available to on site installers. Typically the additional sealants consist of aluminum oxide crystals embedded in a UV cured urethane coat.
Because the surface seal is stronger and more durable when it is applied at the factory, the maintenance of these floors is easier. They tend to be slightly more impervious to stains, moisture, and other discolorations. In addition, the fact that the treatment will last longer, means that you will not have to go through the time, mess, and expense of getting the floors refinished as often. At the same time you will always have the option of sanding down past the factory applied sealing coat, in order to once more reveal the natural wood to the surface. It can then be treated with any of the on-site finishing techniques.
With pre-finished flooring you get all of the advantages of the factory applied durable surface seal, with the look, beauty, and feel of natural hardwood.