The two primary advantages to hiring a subcontractor are saved time and saved money for a project. With a subcontractor, the work can be done quickly and efficiently by those who specialize in the job at hand. The subcontractor is also likely to cost less than general contractors.
Hiring a subcontractor allows a company to temporarily hire professionals who possess expert knowledge that those within the company do not have. Costs are lowered by dealing with a subcontractor that works in volume in specific areas. Because the subcontractor does a limited job on a large scale, that contractor's costs are typically less, allowing the subcontractor to pass the savings on to the hiring company.