A lot of software licenses are not used and become "Shelfware" because the needs of the purchaser changed or the software never delivered what the purchaser expected. Often, the purchaser thinks that they know what they need as far as feature requirements, but after implementation they can not get their employees or customers engaged to use the application. Also, in time their needs change and the product the bought has not evolved to meet their changing needs.
In summary, there is a lot of risk in purchasing software. Consider if the software-as-a-service (SaaS) model may help your organization minimize risk and decrease the lifetime TCO of an application.