An often overlooked, but critical benefit, of Cloud Computing and SaaS is Maintainability. With on-premise, licensed software, the client is responsible for scheduling upgrades to their vendor software.
This process is inherently labor intensive because the new version of the packaged product must be thoroughly tested in the client's environment. Usually this includes System/Integration testing, Performance testing, and User Acceptance testing cycles. The client must be confident the new version of the software works in their environment AND with all of the interfacing applications.
The process is significantly streamlined with SaaS. The client is relieved of the burden of testing the new software release in their environment, as the SaaS provider handles this for them. Many vendors plan numerous releases a year (most often quarterly in the case of Salesforce.com). With rare exception, the client fires up their SaaS application and automatically enjoys the benefits of the extra features in the new release without any action required.
A word of caution though: If your implementation of a vendor's SaaS application is integrated with one or more external application (be they on-premise or SaaS), you must work closely with the vendor to ensure that no APIs upon which your integrations depend are being depricated as part of this release. If you are dependent upon depricated APIs, you must re-write your interfaces to the new API or your intra-SaaS application business process will fail.
