When it comes to enterprise applications, most companies have to make a decision between the purchase of pre-integrated applications or integrating best in class solutions. As mentioned in this article on ERP Software at Your Service, many all-in-one cloud vendors have developed platforms that third parties can use to create add-on applications to their core solution.
"The job of the integrator is not an easy one because if one system changes or upgrades then the integration may break. This is complicated by the fact that some SaaS/cloud providers dictate when upgrades occur making the integrators job dependent on a third party timeline. (Note, the integrator may require vendor upgrades to comply with their existing interface to eliminate some issues related to upgrades) Further, many mid-range solutions need to be customized for particular industries or vertical markets, so the number of integrations required to reach critical mass can be overwhelming.
"The cost of this complexity will be passed on to the customer through the fees charged by the integrator. These fees are often sizable in the area of thousands of dollars per month."