Occasionally an incompatible or broken plugin can completely stop Confluence from starting up. The current workaround for this is to remove or disable the offending plugin in the database. Being able to start Confluence in Safe Mode (via perhaps a JVM argument) would make this process much easier.

A particularly good example of when this would help is when an upgrade has occurred and there are many possible plugins that could be causing issues. Being able to start up the instance in Safe Mode would allow the admin to enable plugins one by one to identify the cause of the problems.