A good deal of research and case studies have demonstrated that vacancy sensors/settings (manual ON/auto OFF) save more energy than occupancy sensors/settings (auto ON/auto OFF). Some of the primary reasons for this include minimizing false-on occurrences, eliminating lights turning on when someone just quickly steps into and then back out of a space and the fact that people tend to leave their environmental conditions as is unless moved to action by some external stimuli (discomfort, peer pressure, etc.). There's also the additional benefit of providing more control to the occupant of their lighting.
Here's one more example demonstrating this – M.E. GROUP’s Kansas City office. On May 16, 2014 we changed the settings of our occupancy sensors from auto ON/auto OFF to manual ON/auto OFF. The image below shows the energy usage two weeks before and two weeks after this change (date indicated by vertical dashed line). For this time frame, there's a 34% energy savings. Now Memorial Day is included within the post two week time frame, but this is partially offset by the additional lighting used after hours (energy usage indicated in red) as a result of meeting a project deadline. As more time passes, we'll have more data for a better comparison.
Three of the primary reasons for the energy reduction contextually relevant for our office are 1) the elimination of work room lights automatically turning on when someone enters for a brief amount of time, even just to reach in and throw away trash or recycling, 2) the elimination of reception lights automatically turning on as we walk in and out the front door to access the rest room (our reception desk is not manned) and 3) open office lighting kept off for longer periods of time during the day (we have access to daylighting). We’re a high performance building consulting firm and energy conservation is part of our office social/cultural norms. Once the change was made, not only did the vacancy setting take advantage of our tendency to leave environmental conditions as is in general, it also took advantage of the fact that there's been some peer pressure to keep our lights off unless absolutely needed.