The friction-free linking enabled by web services (or any SOA). Loosely coupled services, even if they use incompatible system technologies, can be joined together on demand to create composite services, or disassembled just as easily into their functional components. Participants must establish a shared semantic framework to ensure messages retain a consistent meaning across participating services.
Author Doug Kaye's comparison table, showing contrasting characteristics of tight and loose coupling. The item includes a link to a related discussion on the W3C website.