Last year, the City of McKinney, Texas, in rapidly growing Collin County, just north of Dallas, instituted changes so that many more things could be approved by the P&Z Commission without appearing before City Council, and some things could be approved by Staff without going to P&Z. The main motivation was to lighten the case load for CC and P&Z, and it was successful in that.
The problem after that was that staff was so busy preparing reports for items that had to go to P&Z and/or Council, that staff review items had to wait. So, it actually took longer to get staff review items approved because there was no deadline to do so, unlike Commission/Council reviewed items which had to be prepared for review & disposition on a certain date.
The Planning Department added staff, and focused some staff on just the review of items, and other staff on the more administrative tasks (taking applications, working the counter, post-approval tasks, etc.)
I would say that there have been significant cost and time savings, and a positive response from customers from creating staff approval items since we've focused more manpower on the review/approval tasks.
Sorry I don't have any estimates of how much money/time has been saved.