You can continue to develop, maintain or improve application while they are being used. Testers can be given access to the new version (say a small group of current users) while normal users continue uninterrupted.
Improvements can be “published” to take effect at a specific transition time (i.e. midnight). Improvements can be released in total or a sub-set as needed. For example, assume a change in business practice requires an immediate change to your application while you are prototyping other enhancements. You can create, test and release the required change while leaving your current prototype active with testers.
Who did what to your application is automatically audited.