Hi Stuck_in_an_ATR,
I remember seeing a presentation by Airbus on savings by using Idle Rev and F3.
This link
http://www.cockpitseeker.com/wp-cont...tionIssue2.pdf
Page 27 shows a fuel saving of 8 kgs for a F3 Landing plus 15kgs for Rev idle.
We'll never manage to do a 100% efficient flight every time, but all the simple bits add up.