You get high-quality work, made in the specified time with the following technical product support. Agreement concluded with the IT outsourcing company is a reliable guarantee that the computer system will work and all the problems will be fixed promptly. In addition, all new hardware and software components will be implemented competently and efficiently.
If your employees let you down, the best you can do is to deprive bonuses or fire them. If the company is the executor - it will pay you compensation, as it is clearly stated in the contract. For the company it is the main business and it is interested in maintaining the reputation and market competitiveness.