Offline availability . Applications can operate even when the client system is not connected to the network. Laptops, handhelds, and modem-based computers all benefit. LDC makes the most sense when there is a benefit to distributing the data and code of an application. A lot of folks like it.
People get annoyed with it.
Many ASP's have that same problem. The data and code that make up the Salesforce application become local to your computer. They update when needed. The processing happens both on the server and on your client. The web is a static means of communication, like a brochure, booklet, or newsletter.