• Indoor construction. Assembly is independent of weather which often leads to cost overruns on site-built dwellings.
• The speed of having a home built: these new homes can be constructed in a fraction of the time it takes to build a home "on-site".
• Favorable pricing from suppliers. Large-scale manufacturers can effectively bargain with suppliers for discounts on materials.
• Low waste. With the same plans being constantly built, the manufacturer has records of exactly what quantities of materials are needed for a given job. While waste from a site-built dwelling may typically fill several large dumpsters, waste from a modular dwelling is much less. The ability to have the foundation built while the house is being built in the factory.
• Built to the same building code as on-site-built houses.

The on-site assembly process takes only hours or days, rather than weeks or months as is typical with site-built housing. Once assembled, modular buildings are essentially indistinguishable from typical site-built homes. While mobile manufactured homes often decrease in value over time, a well-built modular should have the same longevity as its site-built counterpart, increasing in value over time.
[Citation: http://en.wikipedia.org/wiki/Modular_home]