Sakai doesn't have a verbose administration feature set and requires institutions to grant too much or too little access for users who shouldn't have full administrative privileges. Delegated Access allows administrative users to choose who can access which sites and which permissions they have and tools they can view. Site access through Delegated Access doesn't effect Sakai performance and doesn't show up in the site's membership list. Only step required for an institution to start using Delegate Access is to add site properties (or leverage existing site properties) to describe the hierarchy.
Delegated Access is a contrib tool, currently in use at a number of institutions including Columbia (2 years in production) (I wish I had a list of all production instances! I know of at least 10 others, but I don't want to post them w/o permission). This tool has been proven to handle scalability as well as functionality. It is built off of wicket and the hierarchy tool and is running in both Oracle and MySql production instances. It is highly customizable with several sakai.properties to taylor the tool to your specific use case. 
Delegated Access is currently deployed on the nightly+experimental server .
Delegated Access is currently maintained by Bryan Holladay and supported by Longsight. Longsight will continue to support this application and hope the community will adopt it as a standard for delegating access to departmental administrators.